C. 100 because a quadrilateral must add up to 360. :)
8x^2 -3 = 2
add 3 to each side
8x^2 = 5
divide by 8
x^2 =5/8
take the square root of each side
x = +- sqrt (5/8)
45 = 90% * x
45 = .90x
45/.90 = x
x = 50
45 is 90% of 50
Fifth root of x is x^1/5 as an exponential expression. . This to the 7th power is
x ^(1/5 * 7) which is x^(7/5). Bringing this to the third power is x^ (21/5) which is your answer.