I personally think it's C I hope it's right if not I'm Sorry
To solve for m we want to get m by itself on one side of the equals sign, with everything else on the other side. First we subtract b from both sides, to get it out of the right side of the equation:
y - b = mx + b - b
y - b = mx
Now we divide both sides by x, to get m completely by itself:
(y-b)/x = (mx)/x
(y-b)/x = m
So m is equal to (y-b)/x.
5. 4inch
6. 6cm
7. Cannot tell
8. 50mm
9. Cannot tell
10. 1.5cm
52 = 50
512= 500
500/50 = 10