Consider goods  and  that are perfect substitutes. The original prices were $10 and $9 respectively.
His income is $720. If one day the price of  is 8$, what will happen 
a. The quantity of  becomes 90 due to income
effect.
b. The quantity of  is 80 due to substitution effects
will grow to
c. The quantity of  is 90 due to substitution effects
will grow to
d. The quantity of  is 80 due to substitution effects
will grow to
e. The above answers are incorrect