Answer is 520
Step by step
Perform Prime factorization for each denominator
8 = 2 x 2 x 2
20 = 5 x 2 x 2
13 = 13
List the primes in multiples for the times shown in the factorization
2 x 2 x 2 x 5 x 13 = 520
Check your work
520 / 8 = 65
520 / 20 = 26
520 / 13 = 40
Problem solved