In this problem you have two unknowns: the weight of a bag of apples and the weight of a bag of oranges.
You have one given equation, which allows you to reduce the number of unknowns by one. This means that you will not be able to tell both the weight of the apples and the oranges, but find a line with possible solutions instead.
e.g. apples weigh 6+2x, oranges 7-3x where x is any real number.
You may narrow the problem down by assuming the weights to be non-negative, but to solve for x you need another piece of information that allows you to eliminate the last unknown.