Answer:
x ≈ 14.7
Step-by-step explanation:
use pythagorean therorem
a^2 + b^2 = c^2
c is hypotenuse and we know the hypotenuse is 21
x^2 + 15^2 = 21^2
x^2 + 225 = 441
x^2 = 216
x = √216
