## Elementary Algebra

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.