We can subtract numbers vertically:
#41.23#
#ul(17.386#
Notice that we need a digit in the top number to line up with the 6 in the bottom number - and so we put in a 0 as a placeholder:
#41.230#
#ul(17.386#
In the rightmost column, we're subtracting 6 from 0 - which will lead to a negative number and not be helpful. But what we can do is borrow from the next column over. The column to the left has numbers that are 10 times the size of the one we're in, and so while the 3 gets reduced down to a 2, the 0 gets 10 added to it:
#41.2cancel3^2cancel0^10#
#ul(17.38color(white)(00)6#
#10-6=4#, so let's put that in:
#41.2cancel3^2cancel0^10#
#ul(17.38color(white)(00)6#
#color(white)(0000000)4#
To the next column where we have #2-8#. Again, we need to borrow from the next column to the left:
#41. cancel2^1cancel3^12cancel0^10#
#ul(17. color(white)(0)3color(white)(0)8color(white)(00)6#
#color(white)(000000)4color(white)(00)4#
And so on...
#4cancel1^0. cancel2^11cancel3^12cancel0^10#
#ul(17. color(white)(00)3color(white)(000)8color(white)(00)6#
#color(white)(00000)8color(white)(000)4color(white)(00)4#
#cancel4^3cancel1^10. cancel2^11cancel3^12cancel0^10#
#ul(1color(white)(00)7. color(white)(00)3color(white)(000)8color(white)(00)6#
#2color(white)(00)3. color(white)(00)8color(white)(000)4color(white)(00)4#
