Please help:P trig is confusing

Solve this system of equations. 12x − 18y = 27 4x − 6y = 10

Jada has a meal in a restaurant she adds up the prices listed on the menu for everything they ordered and gets a subtotal of $42.00. when the check comes, it says they also need to pay $3.99 in sales tax. what percentage of the subtotal is the sales tax

What is the difference between the equations of a vertical and a horizontal line?