Answer:
6160 cm
Explanation:
The distance will be the least common multiple of these numbers. That can be figured by looking at their prime factors and choosing the smallest product that contains them all.
16 = 2⁴
28 = 2²·7
40 = 2³·5
77 = 7·11
The factors we need to include are 2⁴, 5, 7, 11. The product of these is
2⁴ × 5 × 7 × 11 = 6160
The boys will step together again after 6160 cm.