Question 1171981
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<pre>

Let x be the unknown value under the problem's question.


Then the average score is  {{{(86+76+90+x)/4}}}.


So, you have this inequality

    {{{(86+76+90+x)/4}}} >= 70


to find x.


Multiply both sides by 4 and then simplify

    86 + 76 + 90 + x >= 280

    252 + x          >= 280

          x          >= 280 - 252 

          x          >=  28..


<U>ANSWER</U>.  The fourth score must be at least 28.
</pre>

Solved, answered and explained.  And completed.


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