Is this part of the problem?
The table is x=2.5 y=6.25; x=9.4 y=88.36; x=15.6 y=243.36
In solving for x and y of an experiment, first is to get the slope and y-intercept of the line using the first and second points:
y=mx + b
6.25 = m*(2.5) + b
88.36 = m*(9.4) + b
Solving for the two unknowns using systems of linear equations (substitution or elimination method):
m= 11.9; b=-23.5
y=11.9x - 23.5
y=11.9*4-23.5
y=24.1
Therefore when x=4, the approximate value of y is 24.1