First you have to know what x and y mean in the equation. They told you in the problem that x is the avg # of feet the tree grew each month. That means that the number multiplied by x is the number of months.
Y will be the total height. That number is 57.6. When y = 57.6, the number that should be multiplied by x is 16.
The tree starts at 8 ft tall, not 0 feet, so the y-intercept in this equation should be 8, because even when 0 months have passed, it will be 8 ft tall. So you know the equation will have the +8 in it added to the slope times x part.
