Answer:
26.4
Explanation:
You can add Y together because they have the same variable making it 10y
The equation is now 10y - 84 = 180
Add 84 to 180 since on the left side it was -84 (Imagine it crossed a magic bridge and become the opposite of what it is)
The equation is now 10y = 264
Divide the equation by 10 because 10 crossed a "magic bridge" to the other side and became division instead of multiplication
The equation is now solved = 26.4
We can cross check this by adding it to the first equation
3(26.4) + 7(26.4) - 84
which gives us 180
Hope this helps