Need on #6 step by step i'm so confused how this works i always get stuck

To find the variable x, set the two outside equations equal to each other because all sides are equal
x+13=3x+3
13=2x+3
10=2x
x=5

then to find h, you set the equation equal to 90 because that's how many degrees it is
2h-45=90
2h=135
h=67.5

Did u want to find the value of x?