The formula for the surface area is 2(lw + lh + wh). So all you have to do is plug the values in.
Box A:
2(lw + lh + wh)
2( (4x6) + (4x25) + (6x25) ).
2(24+100+150)
2(274)
548=Surface Area
Box B:
2(lw + lh + wh)
2( (9x5) + (9x11) + (5x11) ).
2(45+99+55)
2(199)
398=Surface Area
Box C:
2(lw + lh + wh)
2( (10x5) + (10x8) + (5x8) ).
2(50+80+40)
2(170)
340=Surface Area