HEY THERE !!
As we know that the area of a circle (A)= πr^2
But if we know the diameter then the area is (A)= π/4× D^2 { here D is for diameter}
Here diameter is 10.5 inches.
A => π/4 × (10.5)^2
A => π/4 × 110.25
A => π/4 × 27.5625
A => 86.54625 { because the value of π = 3.14}
So the area of the cirsle whose diameter is 10.5 inches is 86.54625 inches square.
HOPE IT HELPED YOU.