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Let I be the amount of Iwan; B be the amount of Ben.
(1) If Iwan gives Ben 3/5 of his money, then Iwan has 2/5 of his money; Ben has B + .
So, your first equation is
= B + . (1)
(2) Your second equation is
I + = + 70. (2)
These are your setup equations.
The next step is to multiply equation (1) by 5 (both sides) and to multiply equation (2) by 4 (both sides).
In this way, you rid of denominators.
Since you do not ask to solve equations, I will stop at this point.