Area of a triangle = 1/2 * base * height. Plug in your given info and solve.
120 = 1/2 * base * height
Multiply by 2 on both sides. This will cancel out the 1/2 on the right side of the equation and isolate our variables, the base and height. You get:
240 = base * height
There wasn't enough information given on the triangle (at least in your description) for the most accurate answer so your answer just becomes any pair of factors at equal to 240.
1, 240
2, 120,
3, 60
4, 80
6, 40
8, 30
10, 24
12, 20
16, 15
Those are all the possibilities not including fractional factors (ex: 1/4 and 960).