How do you Graph 0=x+1/4y+1/2

How do you determine whether a relationship represented as as graph is linear or nonlinear

The quadratic function h(t)=-16.1t^2+150 choose the graph representation

If 30 lb of rice and 30 lb of potatoes cost ? $27.60? , and 20 lb of rice and 12 lb of potatoes cost ? $15.04? , how much will 10 lb of rice and 50 lb of potatoes? cost?