How is frequency density calculated?

Solve the equations y = x + 1 and y = x^2 - 3x + 4 simultaneously.

How do you simplify the following: (3^2)^3

Solve simultaneously x + y = 1, 2x + 3y =9

If a student wishes to have a ratio of 2:7 red pens to yellow pens in their pencil case: a) if they have 50 pens total what is the maximum amount they can carry with them b) if they have 18 red and 31 yellow what is the maximum amount they can carry