first there are two groups, members and non-members, so you know that there are 4 people who are members, if you subtract 4 from ten that would mean 6 people are non-members. now, for the cost of the members would be (7.50 × 4) + (2.95 × 4) = 41.8$
for the non-member group or would be (9.75 × 6) + (3.95 ×6) = 82.2$ now add 41.8 to 82.2 which equals 124.0$ in total
