Twice the difference of a number and 3 is equal to three times the sum of the number and 7. find the number.

Can some one me with these questions

Consider circle c with angle acb measuring 3/4 radians.if minor arc ab measures 9 inches, what is the length of the radius of circle c? if necessary, round your answer to the nearest inch.

For a function f(x), a) if f(7) = 22 then f^-1(22) = b) f^-1(f(c)) =