We multiply this out as follows. We take each term of the first bracket and multiply them by the second bracket. Then we expand out the result.
(x + 5)(a − 6)
= x(a − 6) + 5(a − 6)
= ax − 6x + 5a − 30
We cannot do any more with this answer. There are no like terms, so we cannot simplify it in any way.