Pls answer asap!! for a test

In the rectangle below ac=30 units what is de

On a string instrument, the length of a string varies inversely as the frequency of its vibrations. an 11-inch string has a frequency of 400 cylces per second. find the frequency of a 10-icnch string.

F(x)=x/2-2 and g(x)=2x^2+x-3 find (f+g)(x)