Question

Jerry is tiling the wall behind his sink. The tiles he's using are square with sides that measure 1 3/4 inches. If the area of wall he's tiling is 42 inches long and 29 3/4 inches high, how many tiles will he need?

Answer 1

S=42*(29 3/4)=4998/4 square inches is square of the wall
4998/4 / (7/4)² = 408 tiles he need
Jerry need 408 tiles for the wall he tiling

Answer 2

First you should find the area of wall he's tiling. You can do it by multiplying its length and height.
$A_w={L}\cdot{H}=42\cdot29\frac{3}{4}=1249\frac{1}{2}=1249,5$

After that, the area of one tile.
$A_t=L^2=(1\frac{3}{4})^2=3\frac{13}{16}=3,0625$

And now remains only to divide area of the wall by area of one tile and that will give us the answer.
$N=\frac{A_w}{A_t}=\frac{1249,5}{3,0625}=408$