Answer:
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![\boxed{ \sf{ \bold{1. \: \: \: x = 5}}}](https://tex.z-dn.net/?f=%20%5Cboxed%7B%20%5Csf%7B%20%5Cbold%7B1.%20%20%5C%3A%20%20%5C%3A%20%5C%3A%20x%20%3D%205%7D%7D%7D)
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![\boxed{ \sf{ \bold{2. \: \: x = 6}}}](https://tex.z-dn.net/?f=%20%5Cboxed%7B%20%5Csf%7B%20%5Cbold%7B2.%20%5C%3A%20%20%5C%3A%20x%20%3D%206%7D%7D%7D)
![\boxed{ \bold{ \sf{3. \: \: x = 21}}}](https://tex.z-dn.net/?f=%20%5Cboxed%7B%20%5Cbold%7B%20%5Csf%7B3.%20%5C%3A%20%20%5C%3A%20x%20%3D%2021%7D%7D%7D)
Step-by-step explanation:
1. ![\sf{3x + 6 = 21}](https://tex.z-dn.net/?f=%20%5Csf%7B3x%20%2B%206%20%3D%2021%7D)
Move constant to right hand side and change its sign
⇒![\sf{3x = 21 - 6}](https://tex.z-dn.net/?f=%20%5Csf%7B3x%20%3D%2021%20-%206%7D)
Subtract 6 from 21
⇒![\sf{3x = 15}](https://tex.z-dn.net/?f=%20%5Csf%7B3x%20%3D%2015%7D)
Divide both sides of the equation by 3
⇒![\sf{ \frac{3x}{3} = \frac{15}{3} }](https://tex.z-dn.net/?f=%20%5Csf%7B%20%5Cfrac%7B3x%7D%7B3%7D%20%20%3D%20%20%5Cfrac%7B15%7D%7B3%7D%20%7D)
Calculate
⇒![\sf{x = 5}](https://tex.z-dn.net/?f=%20%5Csf%7Bx%20%3D%205%7D)
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2. ![\sf{33 = 7x - 9 }](https://tex.z-dn.net/?f=%20%5Csf%7B33%20%20%3D%207x%20-%209%20%7D)
Swap the sides of the equation
⇒![\sf{7x - 9 = 33}](https://tex.z-dn.net/?f=%20%5Csf%7B7x%20-%209%20%3D%2033%7D)
Move constant to right hand side and change it's sign
⇒![\sf{7x = 33 + 9}](https://tex.z-dn.net/?f=%20%5Csf%7B7x%20%3D%2033%20%2B%209%7D)
Add the numbers
⇒![\sf{7x = 42}](https://tex.z-dn.net/?f=%20%5Csf%7B7x%20%3D%2042%7D)
Divide both sides of the equation by 7
⇒![\sf{ \frac{7x}{7} = \frac{42}{7} }](https://tex.z-dn.net/?f=%20%5Csf%7B%20%5Cfrac%7B7x%7D%7B7%7D%20%20%3D%20%20%5Cfrac%7B42%7D%7B7%7D%20%7D)
Calculate
⇒![\sf{x = 6}](https://tex.z-dn.net/?f=%20%5Csf%7Bx%20%3D%206%7D)
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3. ![\sf{28 = 7 + x}](https://tex.z-dn.net/?f=%20%5Csf%7B28%20%3D%207%20%2B%20x%7D)
Swap the sides of the equation
⇒![\sf{7 + x = 28}](https://tex.z-dn.net/?f=%20%5Csf%7B7%20%2B%20x%20%3D%2028%7D)
Move constant to right hand side and change it's sign
⇒![\sf{x = 28 - 7}](https://tex.z-dn.net/?f=%20%5Csf%7Bx%20%3D%2028%20-%207%7D)
Subtract 7 from 28
⇒![\sf{x = 21}](https://tex.z-dn.net/?f=%20%5Csf%7Bx%20%3D%2021%7D)
Hope I helped!
Best regards!!