A = 2(bh/2) + 2lw + bw
2(bh/2) comes from the area of one triangle being bh/2 and there are two triangles (so we multiply bh/2 by 2)
2lw comes from the areas of the 2 rectangle faces
bw comes from the third rectangular face
A = 2(bh/2) + 2lw + bw
A = bh + 2lw + bw
(If you multiple then divide a number by the same thing, you end up getting the same number you started with)
A = (24cm)(5cm) + 2(13cm)(10cm) + (24cm)(10cm)
A = 120cm^2 + 260cm^2 + 240cm^2
A = 620cm^2
Hope this helps!