[tex] \frac{1+3x}{4}= \frac{5}{2} [/tex]
To solve the proportion, we first need to do cross mutiplication.
[tex](1+3x)(2)=(5)(4)[/tex]
[tex]2+6x=20[/tex]
After that, we simply just need to simplify and perform the necessary algebra to solve for the value of x.
[tex]6x=18[/tex]
[tex]x=3[/tex]
ANSWER: B. The value of x is equal to 3.