85 points, please answer ASAP question below, my brain is hating me today, I feel like this is easy but I just can't get it

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 .

The suare root of 9x plus 7 plus the square rot of 2x equall to 7

Of the 304 people who attended a school play, 5/8 were students. how many of the people who attended were students.