s = the number of sodas sold
h = the number of hot dogs sold
A vendor sold a combined total of 252 sodas and hot dogs means:
s + h = 252
The number of sodas sold was three times the number of hot dogs sold means:
s = 3 h
Put this value in equation:
s + h = 252
3 h + h = 252
4 h = 252
h = 252 / 4
h = 63
s = 3 h
s = 3 ∙ 63
s = 189
63 hot dogs and 189 sodas