let

l = the length of the table, l>0

w = the width of the table, w>0

rectangular table is four times as long as it is wide:

l = 4w

the area is 36ft:

l*w = 36

plug l = 4w into the last equation:

4w*w = 36

by solving we find:

w = 3 ft

click here to see the step by step solution of the equation:

l = 4*3

l = 12 ft

the length of the table is 12 ft, the width of the table is 3 ft.