Answer:
B(7,10)
Step-by-step explanation:

The coordinate of the image after being reflected is R(3,4).
When dealing with reflection of a line or shape or a figure in the coordinate plane, especially if it is reflected across the y- axis, you just have to give the opposite of the given (original) x- coordinate in order to give a symmetric figure.
-5/16 + 18/16
13/16 - answer
X represents the length of a deck. There are three parts to this equations. The 1. width, 2. the length, and 3. the 5 feet shorter. Using the key words, y = the width of a deck (uses the term is which means =) So that takes the width part out of the equation. Then, 5 feet shorter means -5 than a number. That takes away the 5 feet shorter part of the equation. That leaves x to equal the length of the deck.