Answer: [DISCLAIMER]: All answers are rounded to the nearest hundredth of a decimal
f(1) = 5.20 ; f(2) = 14.70 ; f(3) = 27 ; f(4) = 41.57
Explanation:
f(1) = (1 + [2×1])

f(1) = (1 + 2)

f(1) = (3)

f(1) ≈ 5.20
f(2) = (2 + [2×2])

f(2) = (2 + 4)

f(2) = (6)

f(2) ≈ 14.70
f(3) = (3 + [2×3])

f(3) = (3 + 6)

f(3) = (9)

f(3) = 27
f(4) = (4 + [2×4])

f(4) = (4 + 8)

f(4) = (12)

f(4) ≈ 41.57