Hi!
-9f + 19 - 1 + f is actually -8f + 18.
To do this we add like terms, -9f and f; and 19 and -1
-9f + f is -8f
19 - 1 is 18
Therefore your answer is -8f + 18
I think the answer your after is 150.

⇒ x - 6 = 2x + 26
⇒ x = -32
⇒ This Equation has One Solution
So, It matches with A in Column B
2. 2 + 6x - 7 = 8 + 2x - 10 + 4x
⇒ 6x - 5 = 6x - 2
As, They are Equations of Parallel Lines. They never meet each other.
⇒ This Equation has No Solution
⇒ So, It matches with B in Column B
3. 15x + 25 = 15x + 10
As, They are Equations of Parallel Lines. They never meet each other.
⇒ This Equation has No Solution
⇒ So, It matches with B in Column B
4. 16 + 8x = 4(2x + 4)
⇒ 16 + 8x = 16 + 8x
As, Both Equations are Same. They Represent the Same Line.
⇒ This Equation has Infinite Number of Solutions
⇒ So, It matches with C in Column B
Let x = the unknown angle
sine of an angle is measure of the opposite leg divided by the hypotenuse.
sin x = 10/21
To now solve for x, we so the inverse of sine.
sin⁻¹(10/21) = x
Plug this into your calculator.
x ≈ 28.44 degrees. This would round down to 28 degrees, option B is your answer.
23. not equivalent because the first row 3x-9y=5 then if you multiplied this equation by 2 it will be 2(3x-9y) = 2(5) so 6x-18y= 10 not 6x-9y=10
24.equivalent because the second row 2y-6x=8 multiplied by 2 is 2(2y-6x)= 2(8) so 4y-12x=16
25. equivalent because the first row 5x+3y=19 multiplied by 2 is 2(5x+3y) = 2(19) SO 10X+6Y=38 and the second row 2x+4y=20 multiplied by 5 is 5(2x+4y)= 5(20) so 10x+20y=100