In order to do this, we have to first know the significant figure rules.
Rule #1: All non-zero digits are significant. (1234)
Rule #2: Zeros in front of a number are not significant. (0.093)
Rule #3: Zeros between non-zero digits are significant. (78309)
Rule #4: Zeros at the end of a number are significant if there is a decimal point in the number. (0.05470)
So by going by the rules, 56.0g has three sig figs, because there is a decimal point.
0.0004m only has one sig fig, according to Rule #2.
1003ml has 4 sig figs, because the zeroes are wedged in the two sig fig numbers.
And lastly, 0.0350s has 3 sig figs because the number after a decimal point counts.