Kaliska is jumping rope. The vertical height of the center of her rope off the ground R(t)R(t)R, left parenthesis, t, right parenthesis (in \text{cm}cmstart text, c, m, end text) 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 jumping, her rope is 0\text{ cm}0 cm0, start text, space, c, m, end text off the ground, which is the minimum. After \dfrac{\pi}{12} 12 π ​ start fraction, pi, divided by, 12, end fraction seconds, it reaches a height of 60\text{ cm}60 cm60, start text, space, c, m, end text from the ground, which is half of its maximum height