How do you solve problem with two variables

In your equations, there is only one variable you're using: y. I do not know what you mean by 2 variables, but probably you copied the wrong equations.  

Anyways  

To solve it, you must know that the sum of all 3 angles of a triangle is 180°.  

To set up the equation, add all three angle measures on one side of the equation, and then 180 on the other side. It should be like this:  

(6y+1)+(4y-7)+(9y+3) = 180  

Now that you're done with the set-up, I assume you know what to do next. We can't always do the work for you. ^_~  

> Add up the measures of each angle.  

> Isolate the equation with only variable on one side and only number on the other side.  

> Substitute each variable y for each angle measure and solve it.  

Hope this helps a lot. ^_^