Answer :

Simple. Substitue "1.3" for x in the given equation y = 2x + 3.

2x + 3 = y
2 * 1.3 + 3 = y
2.6 + 3 = y
5.6 = y

The solution to the equation with the replacement set {1.3} for x is {5.6} = y.
I hope you understand how to solve the equation! :)