You can put this solution on YOUR website! 70% of (boy+girls) = boys
boy + girls = 100%
we know boys take 70% of the total which is (boys+girls)
therefore the remaining 30% must be taken by girls.
Given girls = 540, then 540/(boys+girls) = 30%
Make (boys+girls) the unknown and solve for it.
therefore (boys+girls) = 540/30% = 1800
since we know number of girls then 1800-girls=boys = 1260