Let:
b = minutes spent cleaning the 3 bathrooms
k = minutes spend cleaning the kitchen
He spent the same amount of time cleaning each place, therefore:
k = b
He spent 44 minutes in total, besides he spent 8 minutes putting all the supplies away after:
b + k + 8 = 44
since k = b = m:
m + m + 8 = 44
2m + 8 = 44
Solving for m:
2m = 44 - 8
2m = 36
m = 36/2
m = 18
Therefore, he spent 18 minutes in each room