Let a be the number of general admissions and s be the number of student ID admissions. So a+s=181. We can write this as s=181-a.
Also, 3a+2s=435 considering the cost.
Substitute for s: 3a+2(181-a)=435.
3a+362-2a=435, a=435-362=73, so s=181-73=108.
CHECK 3*73+2*108=219+216=435 OK. So 73 general admission tickets and 108 student ID tickets were sold.