This is a first day cover for Scoutpex '79, the 1st Scout Philatelic Exhibition held at Quezon City from July 4 to 14, 1979, in commemoration of the 25th anniversary of the first national jamboree held at Quezon City in 1954.
It's cancelled at U.P. Diliman Post Office,one of two cancellations (the other is Manila).
There also was an overprinted souvenir sheet for Scoutpex '79.
One of the three sponsors of this event shown on the cachet is the APO Philatelic Society.