$2($a$)$ Determine the drain spacing if drains are located $4$ ft below the ground surface, the depth of the impeding layer is $15$ ft below the ground surface, and the saturated hydraulic conductivity is $0\mathrm{.}25ft\frac{3}{?}$ day. For good plant growth, it is required that the water table be at least $3$ ft below the ground surface, and it will be necessary to remove excess rainfall at a rate of $0\mathrm{.}72in\frac{.}{?}$ day $(5$ points$).$

b$)$ Draw a sketch a diagram to show all the terms of the equation that you will use to solve this problem $(3$ points$).$