Question 1118514
10x + 2 = 7     is an equation.  There is no formula per-se, instead one might wish to figure out what x is.  This is called "solving for x" ( x will typically represent an unknown quantity, and, when it is possible to reduce it to a known value, that's usually what we'd like to do. )<br>

One thing about equations, whatever you do to one side you can do to the other side without affecting the equality:

For instance, subtracting 2 from both sides:
10x + 2 - 2 = 7 - 2<br>

Leaves us with:
10x = 5<br>

Now dividing both sides by 10:
10x/10 = 5/10<br>

Notice that on the left hand side, we have 10x/10 and the tens cancel (or you can say 10/10 = 1) leaving just "one x" on the left, which is just written x by itself:
x = 5/10         <br>

We've solved for x.
Usually, we take one additional step to reduce the  fraction to lowest terms (we can divide a fraction's numerator and denominator by a nonzero number without changing the fraction):
x = (5/5) / (10/5)  = 1/2

Ans:  {{{ highlight(x = 1/2) }}}
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Check:   10(1/2) + 2 = 5 + 2 = 7  (ok)  

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To the student:   Thank you for the nice thank you note.  Feel free to ask more questions.  Also, as tutor @ikleyn says, she and others have posted a lot of lessons here to refresh/enlighten you.   Best wishes.