ContourPlot[1=(y*0.3048-7/10/9.8*1.83^2*100/x)*0.45/0.263,2=(y*0.3048-7/10/9.8*1.83^2*100/x)*0.45/0.263,3=(y*0.3048-7/10/9.8*1.83^2*100/x)*0.45/0.263,{x, 1, 100}, {y, 4, 15}]