It Took 60 Hours to Make the First Unit of a Product

Multiple Choice

It took 60 hours to make the first unit of a product. After the second and third units were made, the learning curve was estimated to be 80%. At $10 per hour, estimate the labour bill for the fourth unit. (Use at least three decimals in the exponent if you use the logarithmic approach.)

A) $400 or less
B) from $400 to $420
C) from $420 to $440
D) from $1800 to $2000
E) over $2000