Need help with economics question.

A firm has a production function represented by: q=L^(.75)K^(.25)

Find a function for how much capital and labor a firm should hire to produce a given level of production in terms of the price of labor,w, and the price capital,r.

Suppose w=15 and r=5. What amounts of labor and capital should the firm choose in order to produce 100 units of this good in the least expensive manner?