Answer
$20$
Work Step by Step
As per the given statement let us consider $a$ be the numbers of 15 dollar entrees or guests and $b$ be number of 18 dollar entrees or guests ordered.
Thus,
$a+b=37$ ...(1)
and $15a+18b=606$ ...(2)
From equation (1), we have $b=37-a$
Plug $b=37-a$ in $15a+18b=606$
$15a+18(37-a)=606$
$a=20$
Hence, the correct answer is $20$.
