What is the work to find out the awnser to find out how many centimeters in a foot

To find how many cm are in a ft, you have to use the method of unit rate:

so we know that 12 in. equals a ft. so,

1 ft

12 in.

and 2.25 cm equals an in. so,

1 in.

2.54cm

then we put the rates together and get:

1ft          1 in.
  X   we cancel out the in. units and get:
12 in.    2.54 cm

Solve and get 1 ft = 30.48 cm

It is the top one. the answer is -7. that is smallest