Peter had 12 baseballs cards he traded 1/2 of his cards with his cousin and 1/2 of his cards with tyrell how many cards did he keep

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 .

What is 20+(5 x 2/5 )+ 3 show your work

What situation is an example of an observational study