(3)(6 points) The fish concentration distribution in a lake is given by C-5t+3x+2y+z, where C represents the fish concentration (number of fish per cubic meter), t the time (min), and x,y;z the spatial coordinates (m). What is the for an observer fixed on a boat travelling on the lake with a velocity of Vx=5 (m/min), Vy=2 (m/min) and Vz=0.