we know that
surface area of the tank=2*area of the base+perimeter of base*height
area of the base=12*6----> 72 m²
perimeter of the base=2*[12+6]----> 36 m
height=10 m
so
surface area of the tank=2*72+36*10----> 144+360----> 504 m²
the answer is
the surface area of the tank is 504 m²