Answer:
Option C.
Step-by-step explanation:
The given equations are


We need isolate one of the variables, such that it appears by itself on one side of the equation.
Isolating a variable in two equations is easiest when one of them has a coefficient 1.
In equation 1, coefficient of B is 1. So, we can easily isolate one of the variables.
The equation is

Subtract 3A from both sides.

Multiply both sides by -1.

Therefore, the correct option is C.
If you choose 10 swimmers and 4 are Stingrays, you can say that Stingrays make up roughly 40% of the swimmers. If 20 Stingrays make up 40% of all the swimmers, we just have to find what number 20 is 40% of. That’s easy enough by cross multiplication:
20/x = 40/100
20/x = 4/10
20/x = 2/5
x = 50.
Double check by multiplying 50 * 0.4. Since 50 * 0.4 = 20, we know we have the right answer. There are about 50 swimmers on this team.
increase the speed is definitely the answer