Answer:
D
Step-by-step explanation:
Area of square=400sq.ft
or,l²=400sq.ft
or,l=(400sq.ft)½
or,l=(20²sq.ft)½
or,l=20ft
Thus,length of square is 20ft.
If length of square is increased by 1 ft then ,
New length=(20+1)ft=21ft
Area of square=(21ft)²
=441sq.ft