Two cell towers are located at coordinates (0,0) and (9,12), measured in miles. What is the distance between the two towers?

Use the distance formula: $d=\sqrt{(9-0)^2+(12-0)^2}=\sqrt{81+144}=\sqrt{225}=15$ miles, choice G. This is a $9$-$12$-$15$ right triangle, which is a $3$-$4$-$5$ triangle scaled by $3$. Choice J ($225$) stops before taking the square root. Choice H ($21$) adds the horizontal and vertical distances, which would be the distance traveled along the grid, not the straight line. Choice F ($10.5$) is half of $21$. The straight-line distance must be less than $21$ and greater than $12$.