An enzyme was tested free, and with each of two drugs, A and B…

Step 1. The fits. The enzyme alone gives $V_{\max} = 50$ µmol/min and $K_m = 4$ mmol/L. Drug A gives $V_{\max} = 50$ and $K_m = 12$. Drug B gives $V_{\max} = 25$ and $K_m = 4$.

Step 2. The kinds. Drug A raises $K_m$ three times and leaves $V_{\max}$ alone, so it is competitive, with $1 + i = 3$. Drug B halves $V_{\max}$ and leaves $K_m$ alone, so it is non-competitive, with $1 + i = 2$.

Step 3. The crossing. Drug A shares $V_{\max}$ with the enzyme alone, so their lines share the y-intercept $1/V_{\max} = 0.02$. They cross on the y-axis.