They sold $200 worth of cars each month because 4 x 50 = <<4*50=200>>200
They made $100 a month off cars because 200 - 100 = <<200-100=100>>100
They sold $400 worth of motorcycles each month because 8 x 50 = <<8*50=400>>400
They make $150 a month off motorcycles because 400 - 250 = <<400-250=150>>150
They make $50 more a month off motorcycles than cars because 150 - 100 = <<150-100=50>>50
#### 50