Verified answer

You need to use parentheses when transposing to Yahoo answers single line format. Your expression should look like this:

[(a+3)/(a^2-9)]/[(4a + 12)/(5a - 15)]

Invert and multiply:

= [(a+3)/(a^2-9)]x[(5a - 15)/(4a + 12)]

Factor:

= [(a + 3)/((a + 3)(a - 3))]x[5(a - 3)/(4(a + 3)]

Cancel like terms:

= 5/4(a + 3)