Half of the trip lasts for 8 * 0.5 = <<8*0.5=4>>4 hours.
During the first half, Martin did 4 * 70 = <<4*70=280>>280 kilometers.
And during the second half 4 * 85 = <<4*85=340>>340 kilometers.
In total Martin traveled 280 + 340 = <<280+340=620>>620 kilometers during his business trip.
#### 620