Trigonometric equations help

[on3winyoureyes]

a.In city A, the electric power requirement is at minimum 50 megawatts at midnight and 90 MW(megwatts) at noon. In city B, the minimum is 50 MW at 6 a.m. and the max is 120 MW at 6 pm. This pattern repeats. Create trigonometric equations for this problem.
b. Use your graphing calculator to determine max total power consumption. Round to the nearest tenth MW.

Work:
Well I know that that to find the amplitude and vertical shift we'd do this:
City A: A=(90-50)/2 = 20 and vert= (90+50)/2=70
so it'd be y=20cos(pi/6)+70
City B: A=(120-50)/2=35 and vert=(120+50)/2=85
so it'd be y=35cos(pi/6)+85

I'm not sure about the period. I think that if the cycle repeats then the period is 12 hours then it'd be 2pi/12 or pi/6. Also, I'm not sure if I should use sin or cos for the equations and whether there's horizontal shift. For the graphing part, don't I just graph the two equations in the calculator and go to calc->maximum?

 

[stapel]

a.In city A, the electric power requirement is at minimum 50 megawatts at midnight and 90 MW(megwatts) at noon. In city B, the minimum is 50 MW at 6 a.m. and the max is 120 MW at 6 pm. This pattern repeats. Create trigonometric equations for this problem.
b. Use your graphing calculator to determine max total power consumption. Round to the nearest tenth MW.

Work:
Well I know that that to find the amplitude and vertical shift we'd do this:
City A: A=(90-50)/2 = 20 and vert= (90+50)/2=70
so it'd be y=20cos(pi/6)+70
City B: A=(120-50)/2=35 and vert=(120+50)/2=85
so it'd be y=35cos(pi/6)+85

Where is the variable in your functions?