If a 5 N and a 15 N forces are acting opposite to one another. Find the resultant force and the direction of action of the resultant force

When the forces acts in opposite direction then the resultant force is equal to the difference of their magnitudes.

Hence,

F_resultant=15-5=10N

When two opposite force acts on a body then the object moves in the direction where greater force is applied.Hence body moves in the direction of 15N

Regards..