3 sin theta = 1.5 when 0 is less than or equal to theta is less than or equal to 4 radians
3 sinØ = 1.5 , 0 ≤ Ø ≤ 4
sinØ = 1.5/3 = .5
the sine is positive in I or II
Ø = π/6 or Ø = π - π/6 which is 5π/6
the period of sinØ is 2π, so adding another 2π to π/6 yields 13π/6 , which would be beyond your upper domain value of 4
Ø = π/6 , 5π/6