Pythagorean theorem - please help

answer:
x = 4[tex]\sqrt{2}[/tex] or 5.6568
step-by-step explanation:
formula: a^2 + b^2 = c^2
a^2 + b^2 = c^2
7^2 + b^2 = 9^2
49 + b^2 = 81
b^2 = 32
b = 4[tex]\sqrt{2}[/tex]
x = 4[tex]\sqrt{2}[/tex] or 5.6568 (exact value)