Answer: B. 
Step-by-step explanation:
The notation to express a dependent variable is given by :-
, where Y is depending variable which is dependent upon x ( independent variable).
The given statement : The distance an airplane travels depends on how much time it spends flying.
Here , Independent variable : Time
Dependent variable : Distance
Then , the notation to express distance (dependent variable) the airplane flies in 20 minutes is given by :-

Answer:
-3-5i
Step-by-step explanation:
Use the percent proportion
21 x
—— = ——
100 300
to solve :
21 x 300 = 6300
6300 ÷ 100 = 63
Answer = 63 of Elmer’s shells are fossilized snail shells :)