10/9, or 1 1/9 lbs of walnuts.
The original ratio of walnuts to fruit is (2/3)/(3/5) and we wish to retain that ratio. So let's set up an equality to express that.
(2/3)/(3/5) = X/1
Now solve for X.
(2/3)/(3/5) = X/1
(2/3) * (5/3) = X/1
10/9 = X/1
10/9 = X
So we need 10/9 pounds of walnuts.