I need the step by step process to solving these Statistics word problems

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 .

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On the day a coffee shop first opened, it had 140 customers. 65% of the customers ordered a large coffee. how many customers ordered a large coffee? enter your answer in the box.