+274 If Biftu gives me a penny, I will have twice as many pennies as he has. If I give Biftu a penny, he and I will have the same number of pennies. How many pennies do I currently have?
+36916 You have 7 to start with Bitfu has 5
x = yours y = b's
x+1 = 2(y-1) and
x-1 = y+1 these are given in the description
re-arrange the second equation x = y+2 sub this into the first equation
y+2 +1 = 2y-2
y + 3 = 2y-2
y = 5 then x = y+2 = 7
