Answer:
$40
Explanation:
You find the LCM (least common multiple). To do this, you can use prime factorization.
(there is an below that shows the prime factorization tree for 8 and 10)
so, the only common prime factor is 2. you use the 2 and multiply with the remaining prime factors.
5*2 --> for 10
2*2*2 -->for 8
becomes
5*2*2*2
if you multiply that out, it becomes 40.
Another method is to just think: "What can they both become after being multiplied by a number?" or "What can 8 and 10 both be?"
Anyway, the answer is 40. Hope this helps!