`` r3 + s3 = u3 + v3 = x3 + y3 '' `` but , '' replied jarrah jambres from the driver 's seat , `` u3 + v3 + w3 = x3 + y3 + z3 '' `` and , '' added jazey joskin from the front passenger seat , `` r4 + s4 + t4 = u4 + v4 + w4 = x4 + y4 + z '' how they 'd laughed !