Question 166290
so if t is the number of minutes the hot water is on.

so hot water is 7.8(t)
   cold water is 12.3(t-2)

these 2 must be equal as stated so 7.8t=12.3(t-2)--->7.8t=12.3t-24.6
so 4.5t=24.6
      t=5.47

so hot water is on for {{{5.47min}}}
and cold water is on for {{{3.47min}}}    (t-2)--->5.47-2