The sum of both digits, of either of two two-digit numbers, in whatever order the digits are written, is 9. the square of either of the digits of either number, minus the product of both digits, plus the square of the other digit is the number 21. the numbers are

Let x be the first digit; let y be the second digit."the sum of both digits, of either of two two-digit numbers, in whatever order the digits are written, is 9.""the square of either of the digits of either number, minus the product of both digits, plus the square of the other digit is the number 21"this is a system of equations: can do  . substituting 9 - y for x in the other equation: using x+y = 9, if x = 4 then y = 5. if x = 5 then y = 4. so the numbers are 4 and 5.