A construction company has equipment that depreciates following $V(t) = V_0 e^{-kt}$, where $V_0$ is initial value and $k$ is the decay constant. A bulldozer costs $180,000 new. After 5 years, its value is $95,000. If the company plans to sell the bulldozer when its value drops to $50,000, how many years after purchase will this occur?