Answer
$d = 4.3m$
Work Step by Step
$K_i= U + E_{th}$
$K_i= mgdsin\theta + f_kd$
$K_i= d(mgsin\theta + μ_kmgcos\theta)$
$K_i= dmg(sin\theta + μ_kcos\theta)$
$d = \frac{K_i}{2mg(sin\theta + μ_kcos\theta)}$
$d = \frac{K_i}{2mg(sin\theta + μ_kcos\theta)}$
$d = \frac{128}{(2)(4)(9.8)(sin30^{\circ} + 0.3\times cos30^{\circ})}$
$d = 4.3m$
