Step-by-step explanation:Call the portion of the job that the large pump can do in 1 hour  = 1/R   where R is the total number of hours that it takes 1 large pump to complete the task   Call the portion of the job that the small pump can do in 1 hour = 1 / r   where r is the total number of hours that it takes 1 small pump to complete the task   And Rate x TIME =  Amt of the job done   So...we have the following system   2*(1/R)*4  + 1*(1/r)*4  = 1   →   8/R  + 4/r  = 1 1*(1/R)*4 + 3*(1/r)*4   = 1   →   4/R + 12/r  = 1   Multiply the SECOND equation by -2 and add it to the first   -20/r  = -1   →   r/20  = 1    so r = 20   hours for one small pump to fill  the pool   And using     8/R + 4/r = 1  to solve for R, we have   8/R + 4/20  = 1 8/R + 1/5  = 1 8/R = 4/5 R/8  = 5/4 R = 40/4  = 10 hrs for one large pump to fill the  pool   So... for 4 large pumps and 4 small pumps working in UNISON, we have.....   The 4 large pumps will fill  4/10  = 2/5 of the pool in one hour  [each fills 1/10 of the pool in one hour] The 4 small pumps will fill  4/20  = 1/5  of the pool in one hour  [each fills 1/20 of the pool in  one hour]  So...in one hour    2/5 + 1/5 = 3/5  of the pool is filled  And...inverting this fraction gives us the total time = 5/3 hrs =  1 + 2/3 hrs =  1 hr 40 minPlease give me the Brainlest