She has 10 liters left. Find 4/9 of 18 by multiplying 4/9 and 18. 4/9 of 18 is 8, so she served 8 of the 18, leaving 10 liters.
Using pythagorean's theorem
a^2+b^2=c^2
a being 3
b being 4
we'll get
9+16=25
where 5 is the hypotenuse and also c.
c^2 = 5^2
W - 2.76 = 6.7
isolate the W by adding 2.76 to both sides of the equal sign
W - 2.76 (+2.76) = 6.7 (+2.76)
W = 6.7 + 2.76
W = 9.46
9.46 is your answer
hope this helps
