A particle moves with a velocity 5i - 3j +6k under the influenceof a constant force F= 20i+10j+15k. What is the instantaneous powerof a particle?

I understand that Power = F . V and we can get solution by P = (5 * 20) + (3 * 10) + (6*15) = 160 J ; however, I don't understandwhy is the solution wrong when I get magnitude of F and V thenmultiply them together to get the power? P = 5* sqrt(29) * sqrt(70)= 225