A piecewise function’s graph is broken up into different pieces or parts where each part of the graph has different functions. In order to make use of this they ask to solve when x = 3. In the piecewise functions above on the right side it gives for what values of x that piece graph covers on a coordinate plane.
In your case, you would need to use
x is greater than or equal to 1, since 3 is greater than 1 and the other options wouldn’t work for x = 3.
Then look left of x is greater than or equal to 1 and apply the rule to your x value of 3. This is x + 1. Which is
3 + 1 = 4. Which makes 4 the answer.