Ok so, he digs 1 1/3 feet every hour. And we're trying to find out how much he digs in 2.5 hours. We can simply multiply 1 1/3*2.5 giving us 3 1/3 feet.
you add c to both side which will then make it 7x=k+c then you would divide 7 from both sides leaving you with x=k+c/7. Except 7 will be under the k and c.
If you take 7.6 and multiply it to 16,412.05 (.076)(16,412.05), you get 1,247.32. You then add the overhead cost of 105 to get 1352.32. (Apex verified too)