First, we need to multiply the expression in brackets by 4. This gives (24a-20)-(9a+1) since 6 x 4=24 and 4 x 5=20. Since we have no terms to simplify in brackets and no more multiplying or dividing, we can collect like terms. 24a-9a=15a -20-1=-21 Therefore our final expression is 15a-21
