Answer
$x=26.25$ thousands of people
Work Step by Step
The formula for the total monthly cost of flights as given below in millions of dollars.
$C=\sqrt {0.2x+1}$
The total cost for June is given as $2.5$ million.
Whereas $x$ is the number of passenger in thousands.
So substituting it into for the month of June,
$2.5=\sqrt {0.2x+1}$,
Squaring both sides
$6.25=0.2x+1$,
$5.25=0.2x$
$x=26.25$ thousands of people
