Here is a crude sketch based on the given information:
26
************************
* *
* *
* A = 618 *
* *
*************************************** -----------
* *
* A = 636 * height x
************************************************-----
50
The area of the trapezoid is 1254, which is (altitude) times (average of bases):
1254 = h((50+26)/2)
1254 = 38h
h = 1254/38 = 33
Since the height of the lower portion is x, the height of the upper portion is 33-x.
Since the formula for the area of a trapezoid is (altitude) times (average of bases), for convenience let 2y be the length of the segment parallel to the two bases. We then have this sketch:
26
************************----------------------
* *
* *
* A = 618 * height 33-x
* 2y *
*************************************** -----------
* *
* A = 636 * height x
************************************************-----
50
Then for the areas of the two trapezoids we have
[1]
[2]
Simplify [1]
[3]
Simplify [2]
[4]
Add [3] and [4]
[5]
Solve [5] for x and substitute in [4]
I leave the rest to you. The numbers work out to give a very ugly irrational value for x, which leads me to believe that the given numbers are not right....