Hey there!
To find the least common denominator, or LCD, you will need to find the lowest possible multiple of 8 and 10 that they both share. Keep in mind that multiples of 10 will always end in a zero, meaning that the lowest multiple of 8 that ends in a zero will be your answer.
8 × 1 = 8
8 × 2 = 16
8 × 3 = 24
8 × 4 = 32
8 × 5 = 40
40 will be your LCD. Hope this helped you out! :-)