(3,-5) is your answer .-.
Answer:
The amount of money A pays is 
Step-by-step explanation:
Let
x-----> amount of money A pays
y-----> amount of money B pays
we know that
------> equation A

so
------> equation B
substitute equation B in equation A and solve for x

a / 75 = 15 / 100
100a = 75 * 15 [cross multiplication]
a = 11.25
i hope this helps!!! :D