How do you simplify variable expressions?

You need to do what's called combining like terms.

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If you have (7x+74y-9z+68) + (9q-2x+19z-60), you group them together,

STEP 1: (7x+74y-9z+68) + (9q-2x+3x+19z-60) ===> (7x+3x-2x)+(74y)+(-9z+19z)+(9q)+(68-60)

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Now, we need to evaluate. All we do is mentally remove the variables, but not really. Work as if they were constants, but only for addition and subtraction.

STEP 2: (8x)+(74y)+(10z)+(9q)+(8)

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Finally, remove the parentheses, and for the sake of tidiness organise the variable alphabetically like shown below, and there is your answer:

ANSWER: 9q+8x+74y+10z+8