Sheila chose the number $4n-3$.
Work Step by Step
Let us start at Hal's number, $n$. To get to Sheila's number, first we must multiply by $4$ because the problem says "4 times the number that Hal chose." This gives us $4n$. Next, we must also subtract $3$ from this product because the problem says "$3$ less than." This gives us the expression $4n-3$, which is Sheila's number.