Shelly uses up a \( 350-\mathrm{ml} \) bottle of shampoo in 7 months. What is the Slope \( = \) What is the unit rate \( = \) Write the equation \( = \) The time \( t=3 \) months, Shampoo \( = \). How long would it takes to use \( 250 \mathrm{ml}= \)

The slope of Shelly's shampoo usage can be found by dividing the total amount of shampoo used by the time in months. So, the slope is \( \frac{350 \, \text{ml}}{7 \, \text{months}} = 50 \, \text{ml/month} \). The unit rate is also \( 50 \, \text{ml/month} \), meaning Shelly uses 50 milliliters of shampoo in one month. The equation for the amount of shampoo left over time can be written as \( S(t) = 350 - 50t \), where \( S \) is the amount of shampoo left and \( t \) is the time in months. For \( t = 3 \) months, \( S(3) = 350 - 50 \cdot 3 = 200 \, \text{ml} \). To find out how long it would take to use \( 250 \, \text{ml} \), we can set up the equation: \( 250 = 350 - 50t \). Rearranging gives \( 50t = 100 \) or \( t = 2 \) months. So it would take Shelly 2 months to use 250 mL of shampoo!