Answer
$5(a+3)(a+4)$
Work Step by Step
Factor out the common factor of 5, then factor the resulting binomial.
$5a^2+35a+60=5(a^2+7a+12)$
The first term in each binomial must be a, since $a^2$ has no coefficient.
The operation in each binomial must be addition, since each term in the trinomial is positive.
$3+4=7$ and $3\times4=12$, so the other two terms are 3 and 4.
Since the two binomials contain the same expression they are written with an exponent of 2,
