The following lines are congruent. What is the value of x

Congruent means "the same value". The easiest way to solve this is to equate their values, using algebraic terms.
[tex]30=x+2x+15\\30=3x+15\\30-15=3x\\15=3x\\15/3=x\\x=5[/tex]
Therefore, [tex]x=5[/tex].