Here's number 5. If you need more explanation just let me know.
Let X represent the length of the chord.
By using Pythagoras' Theorem:
4^2 + (X/2)^2 = 15^2
(X^2)/4 = 209
X^2 = 836
X = 28.91
Answer:
dy/dx at x=6 is 0.334
Step-by-step explanation:
The center difference method requires that the values of the function are given in equal intervals which is the case, and allows one to find the value for x = 6 using those of the function for x = 5.5 and for x = 6.5 as follows:

2/7 ( k+5/8) = 2 and 2/7
2/7 (k+5/8) = 16/7 |multiply by 7
2(k+5/8) = 16 |divide by 2
k+5/8 = 8 |subtract 5/8
k=8-5/8 = 7 and 3/8 = 27/8 = 7.375