Hey there! I'm happy to help!
Complementary angles add up to equal 90 degrees.
So, we can use and solve the following equation.
6x-15+3x+6=90
We combien like terms.
9x-9=90
We add 9 to both sides.
9x=99
We divide both sides by 9.
x=11
We plug this into the value for mZH.
3(11)+6
33+6
39
The measure of angle ZH is 39 degrees.
Have a wonderful day!