What you gotta take from this problem:
What Joe got during break =

What his sister gave him =

What he has total = 10 tadpoles.
Now to assemble this equation:

Now combine like terms to get

Subtract 2 on each side of the equation to get

Now you would divide 5 on each side and get

, however since you can't have a .6 of a tadpole, you would have to round it up to 2.