Answer:
9
Explanation:
They are asking what value of x can you input into 2x+1 so that the outpot is 19.
In other words, you need to solve 2x+1=19.
Subtracting 1 on both sides gives: 2x=18.
Dividing 2 on both sides gives: x=9.
So r(9)=19 since 2(9)+1 is 19.