Since the units are all the same, I'll drop them for the purposes of adding/subtracting the numbers together.
We work from left to right, which means we do this first:
#color(white)(0)9.5#
#ul(17.286)#
#26.786#
Now we can do the subtraction:
#26.786#
#ul(color(white)(0)1.4445)#
See that the #26.786# doesn't have enough digits, and so we put in 0 as a place holder:
#26.7860#
#ul(color(white)(0)1.4445)#
We start from the right and move left. First we have #0-5# which doesn't work, and so we borrow from the 6 next to the 0. The 6 is reduces by 1 to 5 (we've borrowed 1) but because we're getting it from the next place up, it's worth 10 to the next place down:
#26.78cancel(6)^5cancel(0)^10#
#ul(color(white)(0)1.444color(white)(0)5)#
#10-5=5#:
#26.78cancel(6)^5cancel(0)^10#
#ul(color(white)(0)1.444color(white)(0)5)#
#color(white)(0000000)5#
And we can do the rest of the subtractions:
#26.78cancel(6)^5cancel(0)^10#
#ul(color(white)(0)1.444color(white)(0)5)#
#25.341color(white)(0)5#
Giving #25.3415mm#
