Which number is equivalent to 0.00000001: 10 to the seventh power or 10 to the negative seventh power? How do you know?

Neither. Take a look.

. . .
103 = 1000.0
102 = 100.0
101 = 10.0
100 = 1.0
10-1 = 0.1
10-2 = 0.01
10-3 = 0.001
10-4 = 0.0001
10-5 = 0.00001
. . .