You will save $9
Convert 20% to decimal
Each % is 0.01 so 20×0.01=0.2
Then multiply
45×0.2=9
5.00+0.67+0.07 that's it I believe
Notice the larger triangle is a right-triangle, and the small one is also a right-triangle. Also notice the "angle tickmark" on each. So both angles have a pair of angles that are equal on each.
the triangles are similar by AA.