Answer: The required number is 70.4.
Step-by-step explanation: We are given to find the number of which 31.68 is 45%.
Let x be the required number.
Then, according to the given information, we have
[tex]45\%\times x=31.68\\\\\Rightarrow \dfrac{45}{100}\times x=31.68\\\\\Rightarrow x=\dfrac{3168}{45}\\\\\Rightarrow x=70.4.[/tex]
Thus, the required number is 70.4.