The answer is c.
(a)
x * 2 = y
2 * 2 = 4
3 * 2 = 6
4 * 2 = 8 not 9
(b)
unknown formula
(c)
x * 3 = y
4 * 3 = 12
5 * 3 = 15
6 * 3 = 18
(d)
x * 4
1 * 4 = 4
2 * 4 = 8
3 * 3 = 9 not 15
C is 2 because you have to move the 5 so you add 5 to 13 which is 18 then divide both sides by 9 so it's 2
C. Heart
this is because the heart is more muscle than anything! Muscle cells have loads of mitochondria and the mitochondria themselves are even more efficient than your average mitochondria.
