You have several pieces of wood.

i.e.

0.83m
1.26m
0.53m
4.09m
3.5m


the total length = m?

get out your calculator and add them up!

Or, type the sum into google, or any of many fine online calculators.
Show some effort, yeah?

To find the total length of the pieces of wood, you need to add up the lengths of each individual piece.

Let's list the lengths of the pieces of wood:
0.83m, 1.26m, 0.53m, 4.09m, 3.5m

To find the total length, simply add up all the lengths:
0.83 + 1.26 + 0.53 + 4.09 + 3.5 = 10.21m

So, the total length of the pieces of wood is 10.21 meters.