First, we need to find the area of the sidewalk that he will be shoveling:

In this case, l=2m and w=40m. Then we have

We know that he can shovel

in 10 minutes, so this would take him 40 minutes since 20*4=80. Now we just need to figure out how much this will cost. Since he charges $5.00 per half hour, we need to get 40 minutes in terms of half hours:

Last, we just multiply his half-hour rate by the amount of half hours he is shoveling for:

I'll let you simplify the fraction.