Answer
91 or higher
Work Step by Step
Let the score on the fourth text be $x$.
Since the average of the four tests must be 88 and the formula of an average is Average=(Sum of numbers)/(Number of numbers), we write the equation as follows:
$88=\frac{85+90+86+x}{4}$
$88(4)=85+90+86+x$
$352=261+x$
$352-261=x$
$x=91$
Therefore, the score on the 4th test must be 91 or higher in order to have an average of 88 or higher.
