Let's say the point is C, so C partitions AB into two pieces, where AC is at a ratio of 3 and CB is at a ratio of 7, thus 3:7,

You first multiply 6 and 8 to see how many people are put in the vans without rented a van. This would equal 48. You then subtract 48 from 59 to see how many people still need to be in a van. This would leave you with 11 people. Then you divide 8 from 11 to get 1 3/8. This means you need 2 vans to fit everyone.
You can translate to:
F ÷ 28 = 24
F/28 = 24 Cross Multiply
F = 28 * 24
F = 672
So, 4 x 3 is 12, so 4 blades cost 79.74 x 3 (because every turbine has 3 blades each) is 318.96