5 Skilled workers can build a wall in 20 days, 8 semi-skilled workers can build a wall in 25 days; 10 unskilled workers can build a wall in 30 days. If a team has 2 skilled 6 semi-skilled and 5 unskilled workers, how long will it take to build the wall?
(a) 20 days (b) 18 days
(c) 16 days (d) 15 days