voltage divider circuit design
With a divider that has R1 = R3 and R1 = 1.2 * R2, you will scale the 8V to -8V range to 0 to 5V, as shown in the plot below.

At Vin = 8V you have a voltage divider with R1 || R3 and R2.  At Vin = -8V, if R1 = R3, you have Vout = 0V.  Doing the math from these two cases gets you R1 = 1.2 * R2.