We need to use law of parallelogram of vector addition. For two vectors #vecP and vec Q# having an angle #theta# between the two the resultant vector #vecR# is given by
#|vecR|=sqrt(|vecP|^2+|vecQ|^2+2|vecP||vecQ|costheta)#
and angle of the resultant #alpha=tan^-1((|vecQ|sintheta)/(|vecP|+|vecQ|cos theta))#
Inserting given values we get
#|vecR|=sqrt((6000)^2+(6000)^2+2xx6000xx6000xxcos60)#
#=>|vecR|=sqrt((6000)^2+(6000)^2+2xx6000xx6000xx0.5)#
#=>|vecR|=6000sqrt3#
#=>|vecR|=10392.3N# rounded to one decimal place.
and #alpha=tan^-1((6000xxsin60)/(6000+6000cos 60))#
#=>alpha=tan^-1((sqrt3/2)/(1+1/2))#
#=>alpha=tan^-1(1/sqrt3)#
#=>alpha=30^@# measured as per measurement of #angle theta#
