In several mathematics tests in one semester, if Xiao Ming scores 81 in the last test, his average score is 87; if he scores 89 in the last test, the average score can be increased by 2 points; If the average score of the test reaches 90 points, what is the minimum score he should take in the last test?
小明在一个学期的几次数学测验中，如果最后一次考81分，则平均成绩是87分；如果最后一次考89分，则可将平均成绩提高2分；若他想在整个学期中的数学测验的平均成绩达到90分，则他最后一次至少要考多少分？
<gadget id="calculator">90 - 89</gadget>
<output>1</output>

<gadget id="calculator">89 - 81</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">1 * 4</gadget>
<output>4</output>

<gadget id="calculator">89 + 4</gadget>
<output>93</output>

<result>93</result>