Since the two parts are in the ratio 5:3, then let the first number be 5x and second number be 3x. As second number is 10 more than the other, so it will be 3x+10.
5x=3x+10
2x=10
x=5
The first number becomes 5(5)=25 and second number becomes 3(5)=15.
The new number will be 25+15=40.