I need help with this problem I need to know how to solve it

I need help with this problem. I need to know how to solve it by hand with no programming to check my solution. This is a mechanical engineering machine analysis homework problem.

Solution

Proposals for a parking ramp having been defeated, we plan to build a parking lot in the downtown urban renewal section. The cost of land is 200W + 100D, where W is the width along the street and D the depth of the lot in meters. The available width along the street is 100m, while the maximum depth available is 200m. We want to have at least 10,000m2 in the lot. To avoid unsightly lots, the city requires that the longer dimension of any lot be no more than twice the shorter dimension. Formulate the minimum cost design problem.