Intai incepem cu transformarile:
32dal=320l
4hl=400l
9dal=90l
80kl=80000l
1 minut ------------------- 320l
13 minute -------------- x
x=320 * 13=4160l
1minut -------------- 400l
15 minute------------y
y=15*400=6000l
6000l+4160l=10160l
80000l-10160l=69840l
1 minut ------------ 90 l
n minute ----------- 69840l
n=69840/90=776 minute