I need help solving the interval notation Im so confused

Solve the system of equations y= 3/2 - 1, -x+ y =-3

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)

There are a total sales of 2,000 dollars on monday on tuesday sales dropped 10% on wednesday sales dropped another 20% compared with tuesday from wednesday to thursday sales increases by an equal amount to 25% of monday total sales what is the net change in dollars on total sales from monday to tuesday