Live in Nevada, work in California some of the time

I live in Nevada and work 5 days a week. 2 of those days, I make a drive to California to do my work. The other 3 days I work in the Nevada office. For simplicity, let's say I make 100k a year and California has a flat tax rate of 10% and Nevada has a tax rate of 0%.

What will my state taxes be?

Will it be:

1. 2/5 * 100k * 10%

2. 100k * 10%

3. 0

Or some other amount? Also, how do I fill out the forms properly?