(15 - 2x2)/4x is the correct answer. The answer you got is not.
6x/2(x-3) ÷ 4x2/5(x+3) - x/2
= 6x/2(x-3) · 5(x+3)/4x2 - x/2 [Invert the denominator (divisor) and multiply]
= 15/4x - x/2
= 15/4x - (x/2)(2x/2x) [Put over common denominator of 4x]
= 15/4x - 2x2/4x
= (15 - 2x2)/4x