Answer:
21.3
Explanation:
It's easier to see how to do this if you transfer the 11 to the bottom of the rectangle. The look at the left triangle. It has 3 sides.
24, 11, and a.
You should be able to find a using
a^2 + 11^2 = 24^2 Expand the squares
a^2 + 121 = 576 Subtract 121 from both sides
a^2 = 576 - 121
a^2 = 455 Take the square root of both sides.
sqrt(a^2) = sqrt(455)
a = 21.33
or
a = 21.3