First, plug the decimals into equation.
Sebastian went 4.5 miles away from his house, then 2.4 miles closer to his house. We can show this with the equation: 4.5 - 2.4
He then hiked 1.7 miles away from his house, so add 1.7 to the equation: 4.5 - 2.4 + 1.7.
Solve.
4.5 - 2.4 = 2.1
2.1 + 1.7 = 3.8
Sebastian hiked 3.8 miles away from his home in total.