Turn the percentage into a decimal
7.5%=0.075
.075x=7.38
Divide both sides by .075 to isolate x
x=98.4
For this case what you should know is that both functions are of the potential type.
We have then that
y = 2 * 2 ^ x This function grows exponentially upwards.
y = -2 * 5 ^ x This function grows exponentially downwards.
Answer See attached graphics.
The outlier is a because it is the most different value compared to the rest.