A 10 N force acts South and a 70 N force acts due East on a 15 kg object.

Add these two forces graphically and show the resultant force

What is the magnitude of the resultant force?

Calculate the magnitude of the acceleration

You need to translate "South" and "East" into directions.

Draw a quadrant (up=north, right=east, left=west, down=south) and impose a coordinate system, with positive x axis corresponding to east and positive y axis to north. Under these coordinates you have that
the resultant is a force with x component 70N and y component -10N.

The magnitude is 50\sqrt{2} , and for the acceleration use F=ma .