Determine the ordered pair that satisfies the equation, 7x-1y=8

When you answer this can you explain

Acircle has a circumference of 28.36 units what is the diameter of the circle

Gabriel determined that his total cost would be represented by 2.5x + 2y – 2. his sister states that the expression should be x + x + 0.5x + y + y – 2. who is correct? explain.