Holy @$#% THAT LOOKS HARD! Sorry, I can't help I don't know that math yet.
Answer:
Step-by-step explanation:
This question is permutation problem. permutations is the number of arrangements or orderings within a constant group.
The formula for permutation is given as
nPk = n!÷(n-k)!
Where n is the number of objects, k is the is the number of objects we want to chose from.
Solution to the question
15P8 = 15!÷(15-8)!
= 15!÷7!
= 15×14×13×12×11×10×9×8×7×6×5×4×3×2×1÷7×6×5×4×3×2×1
= 259459200
Answer:

Step-by-step explanation:
1. Combine like terms
2y-7y = -5y
-5y=5
2. Divide by -5 and the answer is 
When there is a midpoint in a line segment, the two segments that are then produced have to be equal. So that means that because E is a midpoint of DF, DE=EF.
Set up the equation.
DE=EF
2x+4=3x+1
Then solve for x.
x=3
Then plug it back in the equation to find DE and EF.
DE=2x+4=2(3)+4=10
Because DE=EF then EF is also 10.
DF is made from the addition of DE and EF so DF is twice EF.
DF= 20
DE= 10, EF= 10, DF= 20
Hope this helps.