我想問一條數學(F.1)

assume John's savings is $x, then his sister's saving is $(x-300)
After giving $450 from his savings to his sister, John's saving becomes 2/5 (2分之5) of his sister.
x-450=2/5(x-300+450)
5x-2250=2x+300
3x=2550
x=850
Therefore .thier saving is x+(x-300)=2x-300=2(850)-300=$1400

Let x be John's saving,his sister should be x-$300.
then:(x-$450)/(x-$300+$450)=2/5
5x-$2250=2x+$300
3x=$2550
x=$850
So they saving altogether should be:
=x+x-$300
=$850+$850-$300
=$1400