Exercise 1 Page 73

The key phrase is "...less than..." This indicates that we should subtract one thing from another. The term that we are subtracting is "four," it should be on the right-hand side of the subtraction. "Three times a number $n$" tells us to multiply $n$ by $3.$ Now we can complete our expression. Note that this is only one of multiple ways to algebraically express the given verbal expression.