Write it as an equation:
X - 10 = 6x + 3
Now solve for x:
Subtract 3 from both sides:
x-13 = 6x
Subtract 1 x from both sides:
-13 = 5x
Divide both sides by 5:
x = -13/5
For this one you can use 3/8 + 3/8 since 3+3 is equals to 6 and the 8 stays as it is.
I hope this helps.
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