What is the value of x in the equation 3x-y = 30, when y = 15?

Explanation:

Okay so we can start by substituting in as we know what it is already:

Now at this stage we could use a calculator to figure out what of are though a bit of mental math is as easy:

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okay so now we have:

 add 10 to both sides to get rid of the

let's get rid of that fraction by multiplying by

 and there's the solution for x

We can check we got this right by substituting it back into the original equation with the known y:

now,  and we already know what out of is so :

that means

which is ✓

Therefore we know our solution is right.

6/20

step-by-step explanation:

step-by-step explanation:

the answer is 128