Elementary Algebra

$x=3$
Let the unknown number be $x$. The sum of 4 and three times this number is represented by the expression $(4+3x)$. The sum of this number and 10 is represented by the expression $(x+10)$. Since the sum of 4 and three times a certain number is the same as the sum of the number and 10, we obtain: $4+3x=x+10$ $3x-x=10-4$ $2x=6$ $x=\frac{6}{2}=3$