For the potential-energy diagram in (Figure 1), what is the maximum speed of a 5.0 g particle that oscillates between x = 2.0 mm and x = 8.0 mm?

Question

parabola starts at 5,2 and ends at 5,8 with the bottom at 1,4

Answer 1

5 what, Joules? if between 2 and 8 the middle should be at 5, not at 4. I do not understand.
If the maximum is 5 Joules and the minimum is 1 Joule, the potential energy drops by 4 Joules from max to min. That means the kinetic energy increases by 4 Joules between stop at the ends and full speed at the minimum
That means (1/2) m v^2 = 4 Joules