Rosa is buying school supplies. uf she needs x number of notebooks and each notebook cost a dollar and she needs y number if pens that cost b dollars, each write an equation for t, the amount of dollars she will spend

At the beginning of 1974/75,2 years a man invested #2000 in a bank at 12.5% compound interest, if it degree #650 at the end of each two years to pay his son's school fees, after payment of interest to pay his son's school fees, how much did he have left at the beginning of the 1978/79 school year?