Question

Solve for x.



7
12
21
4

Answer 1

x² + 14² = (2√85)²
x² + 196 = 340
x² = 144

x = 12

The second option is your answer. 

Answer 2

Pythagorean Theorem
a^2 + b^2 = c^2
or
a^2 = c^2 - b^2

in this case:

x^2 = (2√85)^2 - 14^2
x^2 = 340 - 196
x^2 = 144
x = 12