A wall of a small, pre-fabricated shed has the dimensions shown above. If ten of these walls need to be painted with two coats of paint and a gallon of paint covers $400$ square feet, then what is the least number of gallons of paint needed in order to complete this task?

$\text{Area of a rectangle} = (\text{length})(\text{width}) $

$\text{Area of a triangle} = \frac { 1 }{ 2 } (\text{base})(\text{height}) $