Question 94·Easy·Linear Functions
The temperature , in degrees Fahrenheit, of a liquid hours after it is removed from a heat source is given by the linear equation .
What is the temperature of the liquid 4 hours after it is removed from the heat source?
For questions with a given linear model, first identify which variable is the input (often time) and what specific value the problem gives you. Substitute that value directly into the equation, then simplify step by step, doing multiplication before addition or subtraction and watching signs carefully. This straightforward plug-in-and-calculate approach is fast and avoids overthinking the context when the function is already provided.
Hints
Match the variable to the quantity
In the equation , which symbol represents the time in hours, and what value should you use for 4 hours?
Use substitution
Take the equation and substitute the value you found for into it. Write the new expression for .
Simplify carefully
After substitution, do the multiplication first, then the subtraction. Be careful with the order of operations and with the sign in front of 5.
Desmos Guide
Evaluate the expression in Desmos
In an expression line, type 90 - 5 * 4 exactly as shown. Desmos will display the numerical result to the right; that value is the temperature after 4 hours.
Step-by-step Explanation
Identify the given time and the correct variable
The equation is , where:
- is the temperature in degrees Fahrenheit.
- is the time in hours after the liquid is removed from the heat source.
The question asks for the temperature 4 hours after removal, so we will use .
Substitute the time into the equation
Replace with in the equation :
Now we just need to simplify this expression.
Simplify to find the temperature
First multiply :
Then subtract from 90:
So, the temperature of the liquid after 4 hours is 70 degrees Fahrenheit, which corresponds to choice D) 70.