An investor enters into a long position in NN futures contracts on an index, where each contract has a notional value of VV times the futures price F0F0. The initial margin is 20% of the notional value for NN contracts. There is no maintenance margin requirement. The margin account earns a continuously compounded interest rate of 10%. The futures contracts are marked-to-market weekly. Assume there are 52 weeks in a year. One week later, the futures price decreases by 15%. Calculate the percent change in the investor's margin account after one week.