The area is the product of the dimensions (length x width).
If the dimensions must be whole numbers and the area is 42 square feet,
then the dimensions can only be . . .
1-ft by 42-ft
2-ft by 21-ft
3-ft by 14-ft
or
6-ft by 7-ft .
6-ft by 7-ft probably makes the most sense for a quilt.