A common theory in such cases is to multiply the prime numbers and then add a certain element to them. In this case, we can follow the pattern:
1 × 5 = 5
2 × 10 = 20
3 × 15 = 45
4 × 20 = 80
Thus, 4 + 4 = 80 could be the answer. If you have another opinion or another model that you think might be correct, let me know!
