Multiply the first equation by a^2:
We still have to clean up the a^3 term, so we multiply the first equation by -5a:
Add the two equations to get:
The value of n is 105.
Hope this helps!
simplfy the fist equation to get a^2+4a=-21 and it can also be (a+4)a=-21 so we get a=-3 since 3+4=7 and -3*7=-21 then we plug a=-3 into the second equation to get 81-(-27)+9=3n which is 117=3n so n=39