Finding Gravity Constant

[BayernBlues]

1. The problem statement, all variables and given/known data

So I need to find the values for local acceleration and frictional force due to a pulley system using the equation below. After graphing acceleration for various ∆mass vs acceleration using Excel, I get the following equation:
y = 0.0144x - 0.0875

I don't understand what the slope and y intercept in this equation represent though, how can I use them to find the 'local acceleration and frictional force'?

2. Relevant equations

a = (∆m/TOTAL MASS)g - (f/TOTAL MASS)

where f = frictional force

3. The attempt at a solution

I think I'm supposed to get the gravity constant from the linear equation, but not sure how. Obviously it's not 0.0144.

[andrevdh]

What did your setup look like?

A hanging load (mass ∆m) pulling a trolley (string passing over pulley) with constant mass (mass m) horizontally? So that TOTAL (ACCELERATING) MASS = ∆m + m?