What is the fomula to calculate Book Value? Please help.

1. A machine that cost $540,000 has an estimated residual value of $60,000 and an estimated useful life of six years. The company uses straight-line depreciation. Calculate its book value at the end of year 5.

Book value: ?

2. A machine that cost $190,000 has an estimated residual value of $19,000 and an estimated useful life of four years. The company uses double-declining-balance depreciation. Calculate its book value at the end of year 3.

What is the Book Value: ?