The product would expand to

This is a trinomial, and the only way to make it a binomial is to cancel out a coefficient using our variable
.
So, we can cancel either the linear term or the constant term.
In the first case, we require

In the second case, we require

But
must be a non-zero rational number, so this solution is not feasible.
First step: Create a common denominator with 1/3
1/3 x 5/5 = 5/15
Second step: Subtract
14/15
-5/15
_____
a: 9/15