a$)$ Naive approach

b$)$ Weighted additive approach with the weights of $0\mathrm{.}15,0\mathrm{.}35,$ and $0\mathrm{.}50,$ respectively

c$)$ Exponential smooting $=0,5$ and $F1=D1)$

a$)$ Calculate MAD, MAPE, MSE values...