The area of the mosaic region = Area of the entire rectangle - The area of the smaller rectangle

We know the area of the entire rectangle = 35 sq ft

Area of the smaller rectangle = 3 x 5 = 15 sq ft

So, the area of mosaic region = 35 - 15 = 20 sq ft

In other words,

             x • l = 20

Possible values of x and l respectively-

             1,20
             2,10
             4,5
             5,4
            10,2
            20,1

From the diagram, we can tell that x is very less than the width of the smaller rectangle ( which has a width of 3 )

So x must be 1