v\text{ (mph)}$ $t\text{ (h)}$ $0$ $20$ $40$ $50$ $60$ $1$ $2$ $3$ $4$ $5$ $6$ $$\text{Area} = 50 \times 4 = 200$

x\text{ (miles)}$ $t\text{ (h)}$ $0$ $100$ $200$ $300$ $1$ $2$ $3$ $4$ $5$ $6$ $$x(4) = 200$