Units digit: A * 8 must end in 4. The only digits for A that work are 3 (8*3=24) or 8 (8*8=64). If A=3, the problem is 633 * 8 = 5064. This matches the format 50B4, with B=6. If A=8, 688*8 = 5504, which doesn't fit. So, A=3 and B=6.