Total these measurements. your answer should indicate the proper accuracy.

your answer should indicate the proper precision (correct number of significant figures).

145.96 m
146.00 m
146.0 m
146.2 m

p. s. totally clueless. .

One way of calculating decimal sum is by using partition

8.3 = 8 + 0.3
5.2 = 5 + 0.2
4.36 = 4 + 0.3 + 0.06
42.1 = 42 + 0.1
86.0 = 86

Add the units together: 8 + 5 + 4 + 42 + 86 = 145
Add the tenth together: 0.2 + 0.3 + 0.3 + 0.1 = 0.9
Add the hundredth together: 0.06 (we only have one value in hundredth)

Then add all the answers together: 145 + 0.9 + 0.06 = 145.96

Answer 145.96 is correct to two decimal places
If we want to round this answer to correct significant figures, it would depend on how many significant figures are asked. 

For example:
145.96 to one significant figure is 100.00
145.96 to two significant figure is 150.00
145.96 to three significant figure is 146.00

and so on

Correct 146.00 (answer is rounded to three significant figures)