Time needed for a point on a wave to move between two transverse displacements

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Homework Statement

If a wave y(x,t) = 5mm sin(kx + (600rad/s)t + φ) travels along a string, how much time does any given point on the string take to move between displacements y = 2mm and y = -2mm

The Attempt at a Solution

we have
1. 2=5sin(kx + 600t₁ + φ)
sin(kx + 600t + φ)=0.4
kx + 600t + φ = 0.4 (=0.4 or =23.5 because I am not sure which mode to use on the calculator, degrees or radians)
2. -2=5sin(kx + 600t₂ + φ)
sin(kx + 600t + φ)=-0.4
kx + 600t + φ = -0.4 (=-0.4 or =-23.5 same reason)

Since its the same point moving up and down, we have the same kx and φ (ill use the 0.4 since both ways my answer is wrong)

0.4 - 600t₁ = -0.4 - 600t₂
600(t₁-t₂) = 0.8
Δt = 1.3 * 10^-3s = 1.3ms

the answer is 1.1ms and its supposed to be one of the easiest problems because its the first problem of the chapter but i just can't do it and please tell me more about the calculator modes issue i talked about

 

[aub]

my answer my be right because i just found out that there are many changes in newer and older versions and that the book has apparently used other close values (like in many other exercices) so it may be that

is what I am doing right?