Step 1:

Number of softwood 2 x 4 boards are to be placed in a rectangular stack.

A softwood 2 x 4 board is actually 1 1/2 in 3 1/2 in.

The smaller dimensions are due to planing and shringkage of roughly cut 2 in x 4 in board that takes place at sawmills.

The reclangular stack of 2 x 4 board is to be 21 in wide and 12 in high.

Thus, area of the each softwoodboard is square inches. \ \

Let the number of boards are placed inside rectangular stack is .

Area of the rectangular stack is square inches.

Therefore,

.

Thus, the number of softwood boards inside the rectangular stack are 48.