Question 1205856
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c = mass of the empty cup, or just the mass of the cup itself ignoring the contents
w = mass of the water (or whichever liquid) inside when 100% full, ignoring the mass of the cup


c+0.40w = is the mass when the cup is 40% full 
c+0.40w = 158.3
solving for c gets us
c = 158.3-0.40w


c+0.60w = is the mass when the cup is 60% full 
c+0.60w = 189.5


Let's plug c = 158.3-0.40w into the other equation 
c+0.60w = 189.5
158.3-0.40w+0.60w = 189.5
158.3+0.20w = 189.5
I'll let the student take over from here. 
Solve that equation to find w.
Hint: The value of w is between 140 and 160.


After determining the value for w, use it to find c.
The last step is to compute c+w to get your final answer.
c+w = mass of the cup when 100% full
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