We will call the number "x", this number is squared, which means that it is elevated to the power of 2 and it is multiplied by 6, this term is then added by 15, therefore the expression is:
[tex]6\cdot x^2+15[/tex]The coeficient is the term that is multiplying the variable, in this case the term multiplying x² is equal to 6. Therefore the answer is "D".
