9?-?2=39

Solution idea: replace the question marks with digits a and b to form a two-digit subtraction. Let 9a - b2 = 39. Compute: (90 + a) - (10b + 2) = 39 → 88 + a - 10b = 39 → a = 10b - 49. For digits b = 0…9, the only choice giving a a digit (0–9) is b = 5, which gives a = 1. Thus the equation is 91 - 52 = 39. Answer: 91 - 52 = 39.