Hello!
The answer is C. formulas
Why?
Formulas are laws o conditions that help us when we are solving numerical problems, we use them to relate number/variables in order to found equivalence between what we are calculating and the information we have.
A formula can include constants, variables and always contain an equality, this last one will help us to establish the needed equivalence to solve numerical problems.
Discarding the other given options:
A. decimals: Incorrect, decimals are a type of number which is not whole numbers.
B. graphs: Incorrect, graphs are graphical tools that we can use to show information or data.
D. percentages: Incorrect, percentages are used to show numerical information as a fraction of 100 units.
E. fractions: Incorrect, like decimals, fractions are a type of number which is not whole numbers, fractions are represented by a division of a number into another, representing just a part of a determinate whole number.
Have a nice day!