A simple answer is that any given trapezoid with height h and length of the parallel lines a and b, is half of a parallelogram with an area of (a+b) x h. Since the trapezoid is half of this, it is h(a+b)/2
The answer is -6 degrees Celsius
Plugging it in, we get (3)(2)+2y=-12 and 6+2y=-12. Subtracting 6 from both sides, we get -18=2y and dividing by 2 we get y=-9 to get (2, -9) since x is first in the pair