Answer= D
1package 7 packages
____________=____________
75 envelopes x envelopes
1x=525
divide both sides by 1
x=525 envelopes
Answer:
Answer for #10:

Answer for #1:

Step-by-step explanation:
In order to solve a simultaneous equation using the substitution method you have to:
Use one of the equation and substitute it into the other equation, in this case equation <em>B</em><em> </em>was substituted into equation <em>A</em><em>.</em>
<em>
</em>
Therefore since x = 1 - y, equation A would be:

Answer:
It's 21.
Step-by-step explanation:
The factors of 9 are 3 and 3. (You need to multiply 3x3 to get 9.) The factors of 10 are 5 and 2. But, if you multiply 3 by 5, which gives you 15, and multiply the other 3 by 2, which gives you 6, and then add 6 to 15, you get 21.