Y and x have a relationship that is directly proportional;
y = 7 when x = 2
when y = 21 and x = ?
y : x
7 : 2
if we multiply 7 wit 3, the answer is 21
3 x 7 : 2 x 3
21 : 6
So, when y = 21, x = 6
Answer:

Step-by-step explanation:
since C = πd, the diameter is 25.
So, the radius is 12.5
Step-by-step explanation:
36 : x :: x : 16
16 x 36 = x2
576 = x2
Taking square root on both sides
24 = x
Your equation is:
(x - 6)² + (y + 8)² = 100
When you plug in (0, 0) into this equation, you get:
(0 - 6)² + (0 + 8)² = 100
(- 6)² + 8² = 100
36 + 64 = 100
100 = 100