13•?+?=8

Interpretations:

1. Two independent digits: 13a + b = 8 with a,b ∈ {0,...,9}

• Since 13a ≤ 8, a must be 0, then b = 8.
• Solution: a = 0, b = 8 (i.e., 13·0 + 8 = 8).

2. The two ? are the same digit/variable: 13x + x = 8

• 14x = 8 → x = 8/14 = 4/7 ≈ 0.5714.

3. General real numbers (no digit constraint): 13a + b = 8

• Infinite solutions: b = 8 − 13a.

Which interpretation did you intend? If you meant digits, the answer is 0 and 8. If you meant the same variable, x = 4/7. If you meant general numbers, any pair (a, b) with b = 8 − 13a works.