Her vertical height H(t)H(t)H, left parenthesis, t, right parenthesis (in \text{m}mstart text, m, end text) off the ground as a function of time ttt (in seconds) can be modeled by a sinusoidal expression of the form a\cdot\cos(b\cdot t)+da⋅cos(b⋅t)+da, dot, cosine, left parenthesis, b, dot, t, right parenthesis, plus, d. At t=0t=0t, equals, 0, when she starts moving, she is at a height of 10\text{ m}10 m10, start text, space, m, end text off the ground, which is as low as she goes. After 20\pi20π20, pi seconds, she reaches her maximum height of 30\text{ m}30 m30, start text, space, m, end text.