**Answer:**

D. 8.57

**Step-by-step explanation:**

Okay I'm not sure if I do these problems correctly, but I always get the right answer.

7/11 = 0.6363...

15/0.6363... = 23.5714...

23.5714...- 15 = 8.57

**Step-by-step explanation:**

We know that...

x+y (from the first pair) corresponds to 8(in the second pair)..

0 (from the first pair) corresponds to x-y (in the second pair)..

Hence,

By simply adding the two equations we get,

Hence,

By substituting x=4, we get that y=4

Hence,

x=y=4

**Answer: 1.91293118277**

**Step-by-step explanation:**

1) square root of 64-1 = 7

2)cube root of 7 = ** 1.91293118277**