Answer
$-45a^{4}$
Work Step by Step
We start with the given expression: $15a^{3}\times-3a^{1}$
We rearrange and regroup the expression using the associative and commutative properties of multiplication: $(15\times-3)(a^{3}a^{1})$
We multiply the coefficients: $-45(a^{3}a^{1})$
To multiply powers with the same base, we add the exponents: $-45(a^{3+1})=-45a^{4}$
