Here is the equation:
![f(x)=4x+1](https://img.qammunity.org/2019/formulas/mathematics/high-school/ljhspc8ho57360mlfh2e4opzra5ra9hy2q.png)
You need to find f(3). To do that, substitute all the x's with 3:
![f(x)=4x+1 \rightarrow f(3)=4*3 + 1](https://img.qammunity.org/2019/formulas/mathematics/high-school/wt70ovmx9g6t67b7q5t6sdwyrpcd7qux7n.png)
The first thing you need to do is multiply 4 by 3. Multiply:
![4 * 3 = 12](https://img.qammunity.org/2019/formulas/mathematics/middle-school/h1mu1ragm9bkjrycxt5v4nyjykqht6c2ju.png)
Here is your new equation:
![f(3)=12+1](https://img.qammunity.org/2019/formulas/mathematics/high-school/zmjht6mc5c5i4s1atz7l84h0wg4p721l1m.png)
To get your answer, you need to add 12 and 1. Add:
![12+1 = 13](https://img.qammunity.org/2019/formulas/mathematics/high-school/c7umvruxnw9pvluadt5wbljdvvg98uc1w7.png)
That means:
![\bf f(3)=13](https://img.qammunity.org/2019/formulas/mathematics/high-school/9hhyz95g2l8mj9nvuk18y1s7rhit31j265.png)
If you have any questions, feel free to ask in the comments! :)