1>theta AC.

APPLY DOT PRODUCT.A.C=AC cos(theta)

or,18=sqrt.(14)*5 *cos(theta)

or,theta=15.81deg.

2>B X C=(3i-4j)x(3j-4k)=(9k+12j+16i)

A.(BXC)=13.

3>follow similarly the rules for cross product.

4>it is very simple if ur concept becomes clear on cross & dot product.