Answer:
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. ^_^