Guess which one is me can’t cheat

Given: x + y = 6. if xe (-15, -6, -1), then which of the following sets of ordered pairs are solutions? © {(-15, -21), (-6, -12), (-1, -7)} [(-15, 21), (-6, , 7)} {(-15, 21), (-6, 12), (-1, -7)}

With alll of except for the 2 that i did already

What is the point of inflection for the function f(x)=2cos4x on the interval (0, pi/2)