You can make an equation for each situation where x is the number of bags and y is equal to the total number of oranges.
5x + 1 = y
4x + 3 = y
With substitution: 5x + 1 = 4x + 3
Solve for x.
5x - 2 = 4x
x - 2 = 0
x = 2
There is 2 bags, so plug that into either equation:
4x + 3 = y
y = 4*2 + 3
y = 11 oranges