Answer:
y = 13
Explanation:
Using Pythagoras' identity in the right triangle.
The square on the hypotenuse is equal to the sum of the squares on the other 2 sides, that is
y² + 84² = 85²
y² + 7056 = 7225 ( subtract 7056 from both sides )
y² = 169 ( take the square root of both sides )
y =
= 13