At a furniture manufacturer, worker a can assemble a shelving unit in 5 hours. worker b can assemble the same shelving unit in 3 hours. which equation can be used to find t, the time it takes for worker a and worker b to assemble a shelving unit together?

Let's define the following variable:
 t = total time it takes to assemble a shelving unit together.
 We then have the following equation:
 1/5 + 1/3 = 1 / t
 Solving the equation we have:
 3t + 5t = 15
 8t = 15
 t = 1,875 hours
 
 the time it takes for worker A and worker B to assemble a shelving unit together is:
 t = 1,875 hours

If there are four friends then each would get, 1.25 or 1 1/4. so this is how i solved 5 ÷ 4 = 1.25 . hope this ; )