Answer:
x^2 - 81
Step-by-step explanation:
There is a formula called the difference of squares, which is
(a+b)(a-b) = a^2 - b^2
Let's assume
number of child tickets sold on saturday is x
number of adult tickets sold on saturday is y
On saturday, twice as many adult tickets as child tickets were sold
so, we get

child admission is $6.30 and adult admission is $9.60
a total sales of $535.50
we get

now, we can plug y=2x

now, we can solve for x


now, we can find y


so,
number of child tickets sold on saturday is 21
number of adult tickets sold on saturday is 42.........Answer
Hi!
The combination of 4 digit numbers using those numbers are: 3, 276; 3, 762; 3, 267; 3, 726; 3, 672 etc. This is pretty easy, now you try.
Hope I helped! Have a nice day!
The best estimate is:
D ) 3 meters.
You can eliminate the others as not making sense.