Six years of quarterly data of a seasonally adjusted series are used to estimate a linear trend

Question:

Six years of quarterly data of a seasonally adjusted series are used to estimate a linear trend model as T̂_t = 128.20 + 1.06t. In addition, quarterly seasonal indices are calculated as Ŝ₁ = 0.93, Ŝ₂ = 0.88, Ŝ₃ = 1.14, and Ŝ₄ = 1.05.

a. Interpret the first and the fourth quarterly indices.

b. Make a forecast for all four quarters of next year

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