4 A school trip is planned for 100 students.
The school uses x type A minibuses and y type B minibuses to transport the students.
The type A minibus can carry 16 students and the type B minibus can carry 10 students.
The school wishes to use no more than eight minibuses.
The school wishes to use at least one type A minibus.
The school wishes to use at least three type B minibuses.

a) Explain why 8x + 5y ≥ 50

b) Write down three more inequalities in x and y.