Answer:

Step-by-step explanation:
The formula is 
<em>We need to solve for
, so we can perform the steps shown below:</em>

Hence, the third answer choice is correct.
Answer:

Step-by-step explanation:
There is <em>one-and-a-half</em> <em>hour</em> in <em>ninety</em><em> </em><em>minutes</em>,<em> </em>so multiply 6 by 15 to get 90, then whatever is done to the bottom is also done to the top, so you <em>square</em> 6 to get 36.
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The number in the blank box should be 44 because it said that "3 times x and 4 times y is 44".
You need to multiply the first equation by 3:
3x + 3y = 39.
Then, subtract the first equation from the second equation:
3x - 3x = 0
4y - 3y = y
44 - 39 = 5
Your new equation should look like this: y = 5
Now, substitute y = 5 into the first original equation:
x + 5 = 13
x = 8
Ans. (x, y) = (8, 5)
80 since he starts off with 38 stamps then gains 6 each month for 7 months (6x7=42) so 42+38=80