a group of 400 ants grow at a rate of 12% every 2 months. write an exponential function, f(x) for every x two month period

Perform the required operations on the following functions given: f(x)= 3-x; g(x)= -2x find g[f(x)]

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 .

How to solve a simultaneous equation involved with fractions?