plz help mathz of f.2

plz help me to naswer the question,if you do not know the answer,plz answer.I need the step.Thank for your help~
1)The formula x=a/y-2y is stored in a computer.Whan the values of a and y are input,th corresponding value of x can be obtained.
If a=2 and y=1 are input,x=0.
However,if we want to obtain the value of a by inputting the values of x and y,another formula is required.
(a)What is the required formula??