Can you with these two questions i'm having hard times in math

Acomputer store bought a program at a cost of $10 and sold it for $13. find the percent markup

Solve the following pair of equations for x and y: ax/b_ by /a= a +b; ax - by = 2ab

The party planning committee has to determine the number of tables needed for an upcoming event. if a square table can fit 8 people and a round table can fit 6 people, the equation 150 = 8x + 6y represents the number of each type of table needed for 150 people.