Suta & futa

If memory serves and the rules haven't changed, FUTA is capped at the first 7,000 of wages each year. If a person has earned, say, 6,500 so far (cumulative this year), then receives another 800, only the first 500 of the 800 would be subject to FUTA tax. The remaining 300 of the 800 would not be hit with FUTA tax, nor would any of this employee's subsequent paychecks for the rest of the year.

Based on this you can see that the first two employees' weekly pay (800 and 400) are hit with FUTA, whereas the third employee has already gone over the cap, and hence his current weekly check is fully exempt.

Note that after this latest round of weekly pay, Employee 1 is at 6,800 cumulative and Emp 2 is at 7,000 cumulative. Thus in the next round of payroll, Emp 1's pay will only be hit with FUTA on the first 200, while Emp 2's pay will be FUTA-exempt.

State SUTA limits vary from state to state, though, but it appears from the problem that it's assumed here that the state in question has the same 7,000 cap as does FUTA.