If a: b :: 3 : 4, then what is (5a+6b): (a-2b)?  Choose the correct answer:  A) 57 : 11  B) - 57 : 11  C) 11 : 10  D) - 39 : 5  E) - 1 : 10

Rationale: "a / b = 3 / 4 dividing numerator & denominator of ' ( 5 a + 6 b ) / ( a - 2 b ) ' by b , [ 5 ( a / b ) + 6 ] / [ ( a / b ) - 2 ] = [ 5 * ( 3 / 4 ) + 6 ] / [ ( 3 / 4 ) - 2 ] = - 39 / 5 answer : d"
Answer: D