Question 1141527
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My approach is <U>THIS</U> :


<pre>
(a)  1 gallon = 3.785 liters;


(b)  1 trillion = 1000 billions = {{{10^12}}}.


(c)  17 trillions gallons of water = {{{17*3.785*10^12}}} liters of water = {{{64.345*10^9}}} cubic meters of water = {{{6.4345*10^10}}} tons of water.    <U>ANSWER</U>
</pre>


The problem's formulation invites to make a lot of unnecessary calculations and conversions - I chose much simpler way.



On the way, I used conversion 


<pre>
    "1 cubic meter of water weights 1 metric ton"
</pre>

which should be known to everyone who studied Science.