Force applied on the car due to engine is given as
[tex]F_1 = 300 N[/tex] towards right
Also there is a force on the car towards left due to air drag
[tex]F_2 = 150 N[/tex] towards left
now the net force on the car will be given as
[tex]\vec F_{net} = \vec F_1 + \vec F_2[/tex]
now we can say that since the two forces are here opposite in direction so here the vector sum of two forces will be the algebraic difference of the two forces.
So we can say
[tex]F_{net} = F_1 - F_2[/tex]
[tex]F_{net} = 300 - 150[/tex]
[tex]F_[net} = 150 N[/tex]
So here net force on the car will be 150 N towards right and hence it will accelerate due to same force.