Explanation

Given the pattern:

12 ∗ 21 = 9 = (2 - 1) × (2 + 1) = 1 × 3 = 3 doesn't fit, but (2 + 1)² = 3² = 9 fits

23 ∗ 32 = 25 = (3 - 2) × (3 + 2) = 1 × 5 = 5 doesn't fit, but (3 + 2)² = 5² = 25 fits

If the pattern is (last digit of first number + first digit of second number)²:

34 ∗ 43 = (4 + 4)² = 8² = 64 doesn't fit, but (4 + 3)² = 7² = 49 fits