There are 3 waves traveling in the +x direction, what is the amplitude, phase and speed of the resulting wave?

y=3cos(14x-2600t)

y=4cos(14x-2600t+1)

y=5cos(14x-2600t-pi/2)

Not to seem ignorant, but i am not sure what it is i am even suppose to do. My initial though was to add the first two together, so my amplitude would be 7, but i am not sure what to do with the phase shift. I thought maybe 7cos1 as new amplitude but nothing online seems to give me any information, everything is in sin and we are being "taught' everything in cos, so i assume things just switch a bit? would the new phase be (1-pi/2) and would the rsulting speed be (2pi/14)(2600/2pi)? much help is appreciated.(Crying)(Thinking)(Crying)