## Algebra 1

$20$
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 $20$.