Respuesta :
P = 12/4 = 3 units per second
N = -8/4 = 2 units per second
so in 30 seconds P moves 3*30 = 90
N moves 2 *30 = 60
90+60 = 150 units apart after 30 seconds
3+2 = 5 units per second
300/5 = 60, they will be 300 units apart in 60 seconds ( 1 minute)