24. One diagonal is 46. We use pythagoras to find the other diagonal. 16^2+b^2=20^2 ;b=12 is half the diagonal. Thus the diagonal is 24 and we have 12*46=552 is the area.

26. 20*21 plus the triangle . We infer it has one side 20 and hypotenuse 29 . Solving, 20^2+b^2=29^2; b=21. Thus 10*21 is the area of the triangle. Thus we have 30*21=630 overall.

28. By 3-4-5 triangles the kit has diagonals 6 and 8. Thus it has area 24. The parallelogram region has height 3 by 3-4-5 triangle so it has area 12. Thus in total we have 36 area.