#### Answer

$3d^3+18d^2$

#### Work Step by Step

We can multiply a monomial by a polynomial using the distributive property, which states that we multiply the term outside the parentheses by each term inside the parentheses and then combine like terms to simplify:
$$3d(6d+d^2)=3d(6d)+(3d)(d^2)=18d^2+3d^3$$To write in standard form, the term with the highest power must come first. This gives us: $3d^3+18d^2$.