PLS HELP!!! What are the coordinates of the point on the directed line segment from (−3,5) to (−1,−7) that partitions the segment into a ratio of 3 to 1?

Iam trying to solve a linear equation for the shoe size of someone 84" tall taking into consideration example 1 is 69" tall with a shoe size of 9 and example 2 is 72 inches tall with a shoe size of 11. i understand that the equation should be y=mx+b and that on the graph the answer is (3,2) but i just don't understand how to create the equation to solve for 84-inches and 60-inches tall questions. after two days, i need .

Find the slope of the line passing through a pair of points

Run a linear regression to determine an equation (y=mx+b y=mx+b)