Wang Xiaoming's family paid a total of 138 yuan for water in the first quarter of this year, of which 48 yuan was paid in March. How much is the average monthly payment for the first two months?
王晓明家今年第一季度共缴水费138元，其中三月份缴了48元．前两个月平均每月缴多少元．
<gadget id="calculator">138 - 48</gadget>
<output>90</output>

<gadget id="calculator">90 / 2</gadget>
<output>45</output>

<result>45</result>