Question

If 3x + 9y = 21 , find the value of 4(x + 3y)

Answer 1

Answer:

25

Step-by-step explanation:

The method that should be used is substitution:

Do this by taking 3x+9y=21 and transforming it to be $y=-\frac{1}{2} x+\frac{7}{3}$

Once you have this, substitute the value of y that we just found into 3x+9y=21 to find the value of x: $3x+9(-\frac{1}{2} +\frac{7}{3} ) =21$

Solve for x. You should get 1.5

Once you have this, Plug in 1.5 for the value of x into the y= equation that we found in the beginning: $y=-\frac{1}{2} (1.5)+\frac{7}{3}$

Solve for y. You should get 1.583 (19/12)

Plug in the values of x and y that we found into the last equation to find its value: 4(1.5+3(1.583))