For finding real solutions to cubic equations and those of higher degree, I find a graphing calculator to be useful. The problem can be cast in the form ...
f(x) = 0
where f(x) is the difference between the product of the integers and 240:
f(x) = x(x +2)(x -5) -240
Then all we need to do is ask the calculator to show the x-intercept. It is x=8.