Answer:
11: 4
12: 3
13: 1
17: 3.000060
18: 5.0 x 10^2
19: 5.0 x 10^6
Explanation:
11: digits between 1&9 are always signifigant even if there are zeros between them
13: Zeros after the decimal do not count unless they represent an exact measurement
18: The decimal point moves forward 2 units so 10^2
