I'll first explain conceptually before giving the direct solution:
When a factor is added directly to the #x# of a function, that is, with parenthesis like you've shown above, it has the same effect as making every single input less by 2.
For example this means that when #x = 0# for #y = 3(x -2)# it is the same as inputting #x = -2# to #y = 3x#.
Naturally, this means that for the shifted function to have the same value as the unshifted one, #x# will need to be #2# more than the input of the unshifted function. This logic can be extended to any modification of #x#: it will always have the opposite effect on the shape of the function. A negative number results in a positive shift and visa-versa.
But to show this directly, consider the x-intercept of each function, the point where #y = 0#:
#y = 3x#
#0 = 3x#
#x = 0#
vs
#y = 3(x-2)
#0 = 3(x-2)
#0 = 3x - 6#
#6 = 3x#
#x = 2#
So before the shift, the y intercept was #(0,0)#. Afterward it was #(2,0)#. This shows us that our function had a shift of #2# in the positive direction!
