The parent function: #g(x) = 6^x#
It has:
#y-"intercept": (0, 1)#
When #x-> -oo, y -> 0# so, there is a horizontal asymptote at #y = 0#, the #x#-axis.
When #x-> oo, y -> oo#.
For the function #f(x) = -2(6^x)#:
#y-"intercept": (0, -2)#
When #x-> -oo, y -> 0# so there is a horizontal asymptote at #y = 0#, the #x#-axis.
Because of the #-2# coefficient, the function turns downward:
When #x-> oo, y -> -oo#.
For the function #f(x) = -2(6^x) + 3#
#y-"intercept": (0, 1)#
When #x-> -oo, y -> 3# so there is a horizontal asymptote at #y = 3#.
Because of the #-2# coefficient, the function turns downward:
When #x-> oo, y -> -oo#.
Therefore the range (valid #y#-values): #(-oo, 3)#