To cover a certain area the builder needs x numbers of 4-in tiles and y numbers of 16-in tiles.
If he will only use the 4-in tiles he will need to replace y numbers of 16-in tiles with the 4-in tiles.
Then we need to know that total number of 4-in tiles in terms of x.
One 16-in tile covers area of 16*16 = 256 in^2
yOne 4-in tile covers 4*4 = 16 in^2
Then we need to find the number of 4-in tiles to cover area of 156 in^2
Then we will divide by 16.
==> 156/16 = 16
Then for each one 16-in tile, we need 16 4-in tiles to cover the area.