All real numbers
In these types of problems x is given already, or at least it contains y usually. In this case x is completely given, therefore it can be SUBSTITUTED in to the other equation to find the system.
First we want to look at the equation and if it can be simplified further, in this case it can. Because all numbers in the equation are divisible by 5 evenly, we can divide them all by 5 and get a new and equivalent equation. The new equation would the look like x-3y=4.
Because our first equation tells us how much x is we only need to substitute in our value to our equivalent equation of system 2. The equation with the plugged in value would look like 3y+4-3y=4.
When we simplify this equation by adding like terms we would get 4=4. This may seem like a problem with no solution but it is NOT. If you were to put in any value (let’s say 30) and put it in our equation before 4=4 it would look like 3(30)+4-3(30)=4 which would still cancel each of the like terms and leave the equation as 4=4.
Therefore, we can say that any number would suffice in this system and mean the system is all real numbers.