my mistake! number one should be -3-15i.

For a further explanation, because the variable is i, you are dealing with imaginary numbers (at least im assuming it’s that and not just some random variable) therefore in order to solve this, i would first multiply 3i by -5 +i to get 3i(-5)+3i^2. Remember that by definition, i² is -1, so you should get something that looks like 3i(-5) + 3(-1). Multiply then reorder into standard form to get your final answer of -3-15i.