Answer: You can solve this using a graphing calculator or an online calculator.
Explanation:
1. Solve each equation for y:
x - 7 = 2y so y = (1/2)x - (7/2)
3x - 21 = 2y so y = (3/2)x - (21/2)
2. Graph the 2 equations
3. Find the intersection using the calculator
They intersect at (7,0). Those values of y make both of these equations true.
You can check this by plugging the values in:
(7) - 2(0) = 7 That's true
2(7) - 2(0) = 21 That's also true
Any values that make both equations true are solutions. Each of these equations is linear, and the lines in the graph just cross once, so there is one solution to this system of equations.