Number 7? No idea how to do this?

Its looks like there is no question here. Find x maybe?
the shaded part is a right triangle so we can use Pythagorean theorem
c² = a² + b²
c is the longest side of the or hypotenuse
so I can write it as m² + m² = 9²
m² + m² = 81
2m² = 81
/2 /2
m² = 40.5
√ √
m = √40.5 (well its actually = or - but since it really measurement its +)
~ 6.39
since x is to ms its 2 x 6.39