Question 260673
a^2+3a-18               a^2+12a+36     factor all terms.
------------   div    ---------------
a^2+6a+9                 a^2+4a-21
[(a-3)(a+6)/(a+3)(a+3)]/[(a+6)(a+6)/(a-3)(a+7)] invert the denominator & mult. 
[(a-3)(a+6)/(a+3)(a+3)]*[(a-3)(a+7)/(a+6)(a+6)] cancel out the (a+6) terms.
[(a-3)/(a+3)(a+3)]*[(a-3)(a+7)/(a+6)]
[(a-3)^2(a+7)]/[(a+3)^2(a+6)] ans.