[填空题]
A small box is held peb twx)mo ,69in place against a rough wall by someone pusgig);nga* * xxu 2qb8hhing on it with a force directed x g ;n)x2gigb8u** aqhupward at 28$^{\circ}$ above the horizontal. The coefficients of static and kinetic friction between the box and wall are 0.40 and 0.30 , respectively. The box slides down unless the applied force has magnitude 13
N. What is the mass of the box?
