[" 104.An eraser weighing "2N" is pressed against the "],[" black board with a force of "5N" .If the coeffi- "],[" cient of friction is "0.4" .How much force "],[" parallel to the black board is required to slide "],[" the eraser upwards "],[[" 1) "2N," 2) "2.8N," 3) "4N," 4) "4.8N]]