The length of a segment with endpoints in (x1, y1) and (x2, y2) is calculated as:
![\sqrt[]{(x_2-x_1)^2+(y_2-y_1)^2}](https://tex.z-dn.net/?f=%5Csqrt%5B%5D%7B%28x_2-x_1%29%5E2%2B%28y_2-y_1%29%5E2%7D)
Then, the distance from E(7,9) to R(1,1) is:
![\sqrt[]{(1-7)^2+(1-9)^2}=\sqrt[]{(-6)^2+(-8)^2}=\sqrt[]{100}=10](https://tex.z-dn.net/?f=%5Csqrt%5B%5D%7B%281-7%29%5E2%2B%281-9%29%5E2%7D%3D%5Csqrt%5B%5D%7B%28-6%29%5E2%2B%28-8%29%5E2%7D%3D%5Csqrt%5B%5D%7B100%7D%3D10)
At the same way, the distance from E(7,9) to D(15,3) is:
![\sqrt[]{(15-7)^2+(3-9)^2}=\sqrt[]{8^2+(-6)^2}=\sqrt[]{100}=10](https://tex.z-dn.net/?f=%5Csqrt%5B%5D%7B%2815-7%29%5E2%2B%283-9%29%5E2%7D%3D%5Csqrt%5B%5D%7B8%5E2%2B%28-6%29%5E2%7D%3D%5Csqrt%5B%5D%7B100%7D%3D10)
Therefore ER has a length of 10 ft and ED has a length of 10 ft, So the area of the triangle is calculated as:

Because ER and ED are the base and the height of the right triangle
Now, we need to transform 50 square feet into square inches as:

Now, the minimum number of stones required is calculated as:

Because every stone cover 29.26 square inches
Finally, the total cost of the stones is:
247 * $0.42 = $103.74
Because every stone has a cost of $0.42
Answers: 1. 10 ft
2. 10 ft
3. 50 ft^2 = 7200 in^2
4. 247
5. $103.74