Let the cost of the bicycle be $x
Since Briana needs $73 more, the present amount of money she has will be $(x-73)
Since Molly needs $65 more, the present amount of money she has will be $(x-65)
Now, combining what they have now, they will be able to buy just one bicycle
This means that;
x - 73 + x -65 = x
2x - 138 = x
2x - x = 138
x = $138
The cost of the bicycle is $138