The perimeter of the base of a regular quadrilateral prism is 60 cm, the area of one of the lateral faces is 105 cm2. find: surface area

The complete question in the attached figure

we know that 
A regular quadrilateral is a shape that has four equal sides, with all the interior angles equals
so
is a square
[perimeter of a square]=4*a
a-----> the length side of a square
60=4*a------> a=60/1-----> a=15 cm

Part A)
 [surface area]=2*[area of the base]+4*[area of one lateral face]
area of the base=a²-----> 15²---> 225 cm²
area of one lateral face=105 cm²
[surface area]=2*[225]+4*[105]------> 450+420-----> 870 cm²

the answer Part A) is
surface area is 870 cm²

Part B)
[volume of the prism]=area of the base*height
height of the prism=area of one lateral face/length side of the base 
height of the prism=105/15-------> 7 cm
[volume of the prism]=225*7-------> 1575 cm³

the answer Part B) is
the volume of the prism is 1575 cm³ 

Then why is the question on here if you know the answer