Let us try to make an expression from the given information:
22 times the number x would be 22x
subtract x from 22 times x would be 22x-x which is equal to 21x
now taking square of difference:
(21x)²
(21x)² =21x * 21x
multiplying 21 with 21 and x with x
21*21 =441
x*x =x²
so
(21x)² = 441x²