The position vectors of P and Q are respectively `vec a and vec b `. If R is a point on `vec(PQ) ` such that `vec(PR) = 5 vec(PQ),` then the position vector of R, is
A. `5 vec b - 4 vec a `
B. `5 vec b + 4 vec a `
C. `4 vec b - 5 vec a `
D. `4 vec b + 5 vec a `
