Gradient of the curve C= (ε_(0) *ε_(r)*A)/d

Hello, i have a table of values for C and d gotten from experiment and the task is to find ε_(r). A plot of C against 1/d is a curve .The gradient D ,where D =ε_(0)*ε_(r)*A from here i can make ε_(r) the subject. values of A and ε_(0) are known

your help will be greatly appreciated . yann.