How can x + 8 = -x + 7 be set up as a system of equations?

y = x + 8
y = -x + 7
y = x + 8
y = -3x + 7
y = x + 5
y = -2x + 11
y = 8
y = -3x + 7

Which math sentence can be used to determine if the triangle is a right triangle?

What is the image of c for a 90° counterclockwise rotation about a? (3, 7) (-1, 3) (7, 3)

From the beginning of the day the temperature rose 15 degrees so that by 4 pm it was 87 degrees. what was the temperature at the start of the day