You should either have Y = 50 + 2X with axes Y and X or P = 50 + 2T with axes P and T. Assuming the latter, choose some values of the independent variable, i.e., T, and compute the corresponding values of the dependent variable, i.e., P. E.g., for T = 1 you get P = 50 + 2 * 1 = 50 + 2 = 52. Then plot the resulting pairs (T, P) on the graph and connect them. As it turns out, the graph of P = 50 + 2T is a straight line, so it is sufficient to find two points. Choose any T1, T2, compute P1 = 50 + 2 * T1, P2 = 50 + 2 * T2, plot (P1, T1) and (P2, T2) and connect them.