Freshmen + Sophomores + Juniors + Seniors = 562
Freshmen + Sophomores + Juniors + 122 = 562
Freshmen + Sophomores + Juniors = 440
Let x = the number of sophomores. There are 16 more freshman than sophomores, so there are x + 16 freshmen. There are 26 more Juniors than seniors, so there are 122 + 26 = 148 Juniors.
x + 16 + x + 148 = 440
Solve for x, the number of Sophomores. Freshmen are x + 16. We already figured out there are 148 Juniors and the problem tells you that there are 122 Seniors.