P,Q and R are three points with position vector i + j , i - j and ai +bj +ck respectively. if P,Q,R are collinear then

If the points with position vectors 60i + 3j, 40i - 8j and ai - 52j are collinear, then a =

If P, Q, R are three points with respective position vectors hati + hatj, hati -hatj and a hati + b hatj + c hatk . The points P, Q, R are collinear, if