Alright, the original problem reads this: Evaluate 7+4(8-x) when x is -2.

The first step is to substitute -2 for x because we were told that x=2. The problem now reads: 7+4(8--2).

Now, there is no such thing as subtraction. It is really the adding of negative numbers. A negative number is the opposite of a positive number. --2 is the opposite of the opposite of 2. Because its the opposite of the opposite, its really just the original number, which is 2. Because of this, we change -- to +, since we are now just adding 2. The problem now reads: 7+4(8+2)

Next, we solve the problem within the parenthesis: 7+4(8+2=10) The problem now reads: 7+4(10).

Now for your question. We multiply 4 by 10 because writing the 4 next to the parenthesis indicates that it is to be distributed to all of the numbers in the parenthesis. Since we only have one number in the parenthesis, this process is just regular multiplication. We do not do anything with the 7 yet because the plus sign indicates that it is to be added to the result of 4(10). You always multiply and divide before you add. The problem now reads: 7+40.

Finally, you add the two numbers to get the final answer. The answer is 47.

I hoped that helped. Its sometimes hard to explain these things without being there in person.
Source(s):
I've completed both Algebra and Geometry.

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