4. At school 45 students take piano lessons. The ratio of the numbers of students who take piano lessons to violin lessons is 15:8. The ratio of the numbers of students who take violin lessons to
clarinet lessons is 8:9.
a) How many students take violin lessons? (2 marks)
b) How many students take clarinet lessons? (2 marks)

Suppose there is a simple index of three stocks, stock abc, stock xyz, and stock qrs. stock abc opens on day 1 with 4000 shares at $3.15 per share. stock xyz opens on day 1 with 5000 shares at $4.30 per share. stock qrs opens on day 1 with 6000 shares at $4.60 per share. the price of stock abc on day 8 begins at $3.50. the price of stock xyz on day 8 begins at $3.90. stock qrs opens on day 8 with a price of $4.50 per share. assume that each stock has the same number of shares that it opened with on day 1. what is the rate of change of this simple index over 1 week?

Can someone answer it, and plot it, for 20 points and brainliest answer? p.s. they're the same ! : )

Which equation results from adding the equations in this system? x+6y=9 and -x+2y=-15