Can this be solved this without sin and cos? My daughter got this homework problem, and I can't seem to solve it. What makes it stranger is they haven't done geometry yet: like no sin and cos stuff. They did do area of triangles, but it seems like this is too advanced.  I am wondering if maybe I am missing some simple trick or something like that.
Here is the diagram:

The instruction are to calculate s1-s2.
Any ideas?  I know if you assume they are right angles you can use cos and sin, but I feel like something simpler should be involved.

While this is probably not the way the problem was intended to be solved, we can do it with almost no calculation.
The area you are trying to compute is the area of the yellow trapezoid in the figure below, which is what is left of the $S_1$ triangle after we cut a copy of the $S_2$ triangle from the upper right corner.

By similar triangles, the original $S_2$ plus the blue trapezoid have the same total area as the copy of $S_2$ plus the yellow trapezoid,
so the blue and yellow trapezoids have equal areas.
But the two trapezoids together fill a rectangle $2\,\mathrm{cm}$ high and $10\,\mathrm{cm}$ wide, with an area of $20\,\mathrm{cm}^2.$
Since the trapezoids are equal, each has half the area of the rectangle,
that is, $10\,\mathrm{cm}^2.$
