This is the following way to solve this problem:
3x-10(x+2)=13-7x
3x-10x-20=13-7x (multiply 10 times what's in the parentheses)
-7x-20=13-7x ( subtract 3x from -10x)
-7x-20-13=-7x ( since the 13 is positive, when we move it to the other
side, we change it's sign, so now we subtract 13 from 20
-7x-7=-7x
-7=-7x+7x ( we do the same thing we did above, now with the -7x)
-7=x
x=-7
Answer: x = -7
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