21.9444....
To solve:
Distance / time!!
You can remember by a triangle...
/D\
| M T |
To find distance, MxT
To find mass, D/T
To find time, D/M
Answer:
the specific heat of the unknown compound is 
Explanation:
Generally the change in temperature of water is evaluated as

Substituting 16.1°C for
and 27.4°C for 


Generally the change in temperature of unknown compound is evaluated as

Substituting 27.4°C for
and 94.3°C for 


Since there is an increase in temperature then heat is gained by water and this can be evaluated as

Substituting 179.1 g for m , 4.18 J/g.C for
(specific heat of water)


Since there is a decrease in temperature then heat is lost by unknown compound and this can be evaluated as

By conservation of energy law
Heat lost = Heat gained
Substituting 306.9 g for
, 8459.6J for

Therefore 

Protons : positive charge , about same mass as neutrons , in the nucleus
neutrons : no charge , about the same mass as a proton , in the nucleus
electrons : negative charge , less mass than protons and neutrons , in orbitals outside of the nucleus
The correct answer is A, since it is the only sensible answer.