S = number of senior tickets
A = number of adult tickets
number of senior tickets sold 32 less than half the number of adult tickets.
S = A/2 - 32 (equation 1)
Sales of senior tickets: S*12
Sales of adult tickets: A*11
Total Sales: S*12 + A*11 = 3864 (equation 2)
Substitute A/2 - 32 for S from equation 1 into equation 2 and solve for A, then use equation 1 to determine S.