If you factor the denominator of the left multiplicand...
[(a-4)(a+3)]/[a(a-4)] you can see that the (a-4)s cancel out leaving:
(a+3)/a
now you have
(a+3)/a * 2a^3/((a+3)(a-1)) so the (a+3)s cancel out leaving:
1/a * 2a^3/(a-1) which is:
2a^3/(a(a-1)) so now a^1 cancel leaving
2a^2/(a-1)
