When p = 12, t = 2, and s = 1/6 , r = 18. if r varies directly with p and inversely with the product of s and t, what is the constant of variation?

Several paint mixtures are made by mixing blue paint and white paint. paint colors blue paint white paint mixture a 5 cups 12 cups mixture b 6 cups 6 cups mixture c 4 cups 12 cups mixture d 5 cups 6 cups which mixture has the highest ratio of blue paint to white paint