Forgive me, but your reply was unhelpful. See another post from someone who also got the correct answer. Thank you all the same. I also figured it out with help, using the determinant method.

>>I tried using the distance from a point (-7,5) to a line
>>(y=mx) but am at a loss.
>>
>
>Distance along would not help. This will serve as an
>altitude in the triangle in question. To find the area you
>also need the base, so you have to find the intersections of
>y = mx with the two given lines. I do not see how the
>geometry here may simplify the problem. It appears to
>laborious to me.