Solve this :

29. Gravitational potential in a region is given by v=(3x+4y+12z) J/kg. The  modulus of gravitational field at ( x=1, y=0,z=3) is

(1) 20 N/kg        (2) 13​ N/kg          (3) 12​ N/kg        (4) 5​ N/kg

Dear Student ,.
we know that the gravitational field strength is given as

E = -∇V

or

E = -[i.(δV_x/δx) + j.(δV_y/δy + k.(δV_z/δz)]

here

V = V_x + V_y + V_z = 3x + 4y + 12z

so, we have

E = -[i.(δ(3x)/δx) + j.(δ(4y)/δy + k.(δ(12z)/δz)]

or gravitational field strength will be

E = 12+4-3=13 N/kg
Regards