Wavelength is usually denoted as letter lambda (λ); it is equal to the speed (v) of a wave train in a medium divided by its frequency (f): λ = v/f. Waves of different wavelengths.
Let x = number of long sleeve shirts
Let y = number of short sleeve shirts
x + y = 200
x/2 + y/3 = 80
Now solve this pair of simultaneous equations to find x and y.