We have a set of measurements:
3.4 m, 10.25 m, 20.2 m, and 19 m
Each measurement has its own number of significant digits. For example 3.4 has two significant digits
20.2 has three and 10.25 has four
We are asked how many significant digits does the SUM of them have.
We cannot think of them as isolated measurements, but as a unique result
3.4 + 10.25 + 20.2 + 19 = 52.85
Note the final result has four significant digits, i.e., the numbers 5, 2, 8, and 5
This is our answer: D:4