Ok, so you know that we can't divide fractions no matter what. The first thing you do is keep the first fraction, then change the divide sign to multiplication ( opposite of division is multi. ) and finallly flip the last fraction to 7/1 .
Here's a video to help you understand that method more ...
https://www.youtube.com/watch?v=uMz4Hause-o
The answer ends up as 6.53333333333
Hope this helps !
The only number not divisible by anything except itself and 1, was C. 7
Answer:

Step-by-step explanation:
Let the function of quantity in the lung of air be A(t)
So 
so, A(t) = Amax sin t + b
A(t) = 2.8t⇒ max
A(t) = 0.6t ⇒ min
max value of A(t) occur when sin(t) = 1
and min value of A(t) = 0
So b = 0.6
and A(max) = 2.2

at t = 2 sec volume of a is 0.6
So function reduce to

and t = 5 max value of volume is represent
so,

when t = 5

so the equation becomes

Answer:
change the equation into one variable.
2 y equals 10 + x
y equals 5 + x by 2
now put that into the second equation
-3x + b parentheses 5 + x / 2 equals 11
-3x+b(5+ x/2)
-3x + b5 + bx/2 = 11