The pythagorean theorem states that the sum of the squares of two legs of a right triangle is equivalent to the hypotenuse.
So:
35^2 + b^2 = 40^2
1225 + b^2 = 1600
b^2 = 375
b = 
b = 19.3649
<u>The missing side's length rounded to the nearest tenth is Option C, 19.4</u>
The way to find the difference between 5y - 3 you have to first do the inverse operation of multiplication which is division.
5y - 3
__ __
5 5
y - 0.6