Please help with physics? Thanks in advance!?

Method 1 :

Take g = 9.81 m/s²
Take all downward quantities to be positive, and upward quantities to be negative.

Initial velocity, u = -3.62 m/s
Acceleration, a = 9.81 m/s²
Displacement, s = 1.80 m

v² = u² + 2as
v² = (-3.62)² + 2(9.81)(1.80) (m/s)²
Speed when she hits the water, |v| = √[(-3.62)² + 2(9.81)(1.80)] m/s = 6.96 m/s


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Method 2 :

Gain in K.E. = Loss in P.E.
(1/2)mv² - (1/2)m(3.62)² = m(9.81)(1.80)
v² - 3.62² = 2(9.81)(1.80)
v² = 2(9.81)(1.80) + 3.62²
Speed when she hits the water, |v| = √[2(9.81)(1.80) + 3.62²] m/s = 6.96 m/s

By assuming her mass is 1kg., you can ignore mass entirely in calculations.
Her inital KE = 1/2 (m*v^2) = 1/2 (v^2) = 6.55 J.
As her feet pass the board descending, she has that same KE. downwards.
By the moment her feet reach the water, she has converted GPE due to height when passing the board descending to KE also.
So the extra KE = (mgh) = (1 x 9.8 x 1.8) = (9.8 x 1.8) = 17.64 J.
Total KE at water = (17.64 + 6.55) = 24.2 J.
Her V at water = sqrt.(2KE/m) = sqrt. (2KE) = 6.96m/sec.
Mass ignored.

She starts out with kinetic energy (1/2)mv^2 where v = 3.62 m/s.
She gains energy mgh where h = 1.80 m. Add that to her initial kinetic energy.

That is her final kinetic energy, so set it equal to (1/2)mv^2 and solve for v.

In all three cases, you'll have to leave m as a variable since you don't know it. But you can divide the final equation by m, cancelling it out, so you don't need to know it.