Finding 'x' in Angle Measures

In the diagram below, two lines, $l_1$ and $l_2$, intersect at point $P$, forming four angles. If the measure of angle $1$ is $3x + 15$ degrees and the measure of angle $2$ is $5x - 5$ degrees, what is the value of $x$?

Remember that angles opposite to each other when two lines intersect are equal.