To convert a decimal to a mixed number: the whole-number part stays; the decimal part becomes a fraction (tenths -> /10, hundredths -> /100, thousandths -> /1000), then simplify.

Whole part	=	4
Decimal part	=	0.85 = \(\frac{85}{100}\)
Simplify	=	\(\frac{85}{100} = \frac{17}{20}\) (divide by 5)
Mixed number	=	4\(\frac{17}{20}\)