Question 507026
Let the scores of the first three tests be a, b, and c.  Then:
{{{(a+b+c)/3 = 87}}} To find the sum of the first three test scores, multiply both sides by 3.
{{{a+b+c = 261}}} Now let the fourth test score be x, so...
{{{(a+b+c+x)/4 >= 90}}} Substitute {{{a+b+c = 261}}}
{{{(261+x)/4 >= 90}}} Multiply both sides by 4.
{{{261+x >= 360}}} Subtract 261.
{{{x >= 99}}}
Takia must score at least 99 points on the fourth test to achieve an overall average of 90.