Answer
Double Rooms: $53$
Single Rooms: $27$
Work Step by Step
Let No. of Double rooms be $x$
No. of Single rooms be $y$
Given,
Total No. of rooms $80$
$x+y=80$
$y=80-x$ Equation $(1)$
Charges for double room: $90$ dollars per day
Charges for single room: $80$ dollars per day
Total Charges for $80$ rooms is $6930$ dollars per day
$90x+80y=6930$ Equation $(2)$
Substituting Equation $(1)$ in Equation $(2)$
$90x+80y=6930$
$90x+80(80-x)=6930$
$90x+6400-80x=6930$
$10x=6930-6400$
$10x=530$
$x=53$
$y=80-x$
$y=80-53$
$y=27$
Double Rooms: $53$
Single Rooms: $27$
