We need to isolate a in this equation.
Step 1: Subtract g from both sides
t - g = -0.0035a + g-g
Step 2: We need to divide both sides by -0.0035 to get a to stand alone
(t-g)/(-0.0035) = a
A cleaner, more conventional way of writing this is to get rid of the negative sign in the denominator. In order to do this, we have to apply the negative sign to the variables in the numerator. We can do this by multiplying the numerator and denominator by -1
(-g)(-1) = g (t)(-1) = -t
We can rearrange so it looks neater and the equation becomes (g-t)/0.0035