We have an object measured in Meters, and we want to cut sections of it off in Centimeters, a different unit of measurement.
Because we're subtracting sections of the pipe, we want to make the units the same, this will make our calculations easier.
1 Meter = 100 Centimeters, so, 2.5 Meters = 250 Centimeters
We're cutting ( 60 Cm + 35 Cm + 90 Cm ) off, which totals 185 Cm.
250 Cm Pipe - 185 Cm Cuts = 65 Cm Pipe Left