Subtraction equals 25= last term +(n- 1)*d/2.

The first item = the last item -(n- 1)*d

Substitute a formula to eliminate the first term =[2 last term -(n- 1)*d]*n/2= last term *n-n(n- 1)*d/2=325.

The last term is eliminated in two forms: 25-(n- 1) * d/2, that is, 25n-(n-1) n * d/2-n (n-1) * d/2 = 325.

Solve n= 13, and further solve d=5.