<PRE><B>Question 1132992</B>
&lt;br&gt;
The average of x, y, z, and 90 is {{{(x+y+z+90)/4}}}.&lt;br&gt;
The average of y, z, w, and 100 is {{{(y+z+w+100)/4}}}.&lt;br&gt;
The problem tells us that the first average is 20 less than the second average:&lt;br&gt;
{{{(x+y+z+90)/4 = (y+z+w+100)/4 - 20}}}&lt;br&gt;
{{{x+y+z+90 = y+z+w+100 - 80}}}&lt;br&gt;
Combine terms where possible and  cancel terms that are identical on both sides of the equation and see if you can see how to get the answer from there.&lt;br&gt;
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Note: the solution by tutor @josgarithmetic contains errors and shows the wrong answer....&lt;br&gt;
Can you see the two errors in that solution?</PRE>