A lab technician needs to make \( 400 kg \) of \( 51 \% \) alcohol solution by combining \( 60 \% \) alcohol solution by mass and \( 40 \% \) alcohol solution by mass. How many kilograms of the \( 40 \% \) solution must be used?
A linear function that models data is described below. Find the slope of the model. Then describe what this means in terms of the rate of change of the dependent variable per unit change in the independent variable. The linear function \( f ( x ) = - 0.41 x + 28.6 \) models the percentage of adults in a country who smoked cigarettes, \( f ( x ) \) , \( x \) years after \( 1997 \) .
The slope is \( \square \) . (Type an integer or a decimal.)