The length of the rectangle is 24 cm. How much will the area of this rectangle increase if its width is increased by 4 cm.

Let the initial width of the rectangle be x, then its area will be:
1) S1 = 24 * x cm2.
After the width was increased by 4 and it became equal to x + 4, the area of the rectangle will be:
2) S2 = 24 * (x + 4) = 24x + 96 cm2.
Let’s find how much the area has increased. To do this, subtract S1 from S2:
3) S2-S1 = (24x + 96) -24x = 96 cm2.
Answer: The area will increase by 96 cm2.