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.

answer: all of the odd numbers were opened

the first person was the one that was opening all of the lockers. since one is odd, this causes all of the odd number lockers to be opened in the end.

b and c

step-by-step explanation: