Which is one of the steps in finding the solution to a system of linear equations by substitution?

Fill in the blank to complete the statement about one step in finding the solution by substitution: ____________ to the second equation the value of the variable found, then solve the resulting equation to find the value of the other variable.

Choose the expression which can be substituted to x in the equation y = x + 6 to find the value of the other variable in the system x + y = 14 and y = x + 6.

Choose the expression which can be substituted to x in the equation x - y =-9, to find the value of another variable in the system x + y = 7 and x - y = -9.

Find the solution to the system -2x + y = 5 and 3x - 2y = -5.

Find solution to the system -2x + y = 5 and -x + y = 2.

If A certain part of the amount of money is invested at 15% and the rest at 10% rate. The total interest after one year is Php3325. If the total amount invested was Php27,000. How much was invested at each rate?