What is the rise of a line that has a run of 20 and a slope of 1

1.)Let x  be the amount invested at rate of 8%.Hence 10000-x will be the amount invested at 9%

2.)we know SI=ptr/100=x*1*8/100                                                                            3.)and other SI=(10000-x)*1*9/100                                                                          4.)he got 875rs as interest  on both investments i.e,                                                                    5)8x/100)+((10000-x)*9/100) =875                                                                                                       6.)On solving this we get x=2500 i.e,2500 is invested at rate of 8% and 10000-x=7500 is the amount invesred at rate os 9%