Introductory Algebra for College Students (7th Edition)

Both expressions have the same value, 27. $3(x+5)=3x+15$
Evaluating $3(x+5)$ when $x=4:$ $3(4+5)=3(9)=27$ Evaluating $3x+15$ when $x=4:$ $3(4)+15=12+15=27.$ What we observe: Both expressions have the same value, 27. $3(x+5)=3x+15$