I don’t know if my diagram explains so I will do so briefly using words.
in part a, you are being asked about the projection of the force F (which is essentially another vector) onto the line l. So the resultant vector should have the same direction (3i + 4j) as l, but lengthwise truncated by a factor of 0.4 (cross product between the two vectors Divided by the length of, according to the formula.
in part b, you are asked to find the perpendicular vector formed upon the projection, which is essentially the perpendicular distance taken into the account of its direction which is that of f (2i+j).
hope it helps
