let b be the number of dollars that my brother has

let m be the number orf dollars that I have

since giving 5 dollars makes the values same meaning that m-5 = b+5

now he gives me 25 dollars and i have twice as much that he has so: 2(b-25) = m+25 or 2b-50 = m+25. which means that 2b = m+25

simplifying the first equation: b = m-10 and substituting it gives 2(m-10) = m+25 which means that 2m-20 = m+25. So i have 45 dollars. The question wants my brothers dollar amount, so we can substitute 45 for m into any equation and find that my brother has 35 dollars