All members of our painting team paint at the same rate. If $10$ members can paint a $100$ square foot wall in $10$ minutes, then how long would it take the $15$ members to paint a $100$ square foot wall, in minutes?
100 ft^2 / ( 10 mem * 10 min) = 1 ft^2 /( mem_ min)
100 ft^2 / ((1 ft^2 /mem_ min) * 15 mem ) = 6 2/3 min