The final answer will be a 3x3 matrix. So you'll have 3 rows and 3 columns.
Along row one, the values are: 10, 15, 20
Along row two, the values are: 45, -5, -35
Along row three, the values are: 55, 25, -15
all of which make up the final answer. Each value in bold is the result of multiplying the outer 5 by each value inside the original matrix given. In a sense, it's like using the distributive property, though we wont be adding any of the values (everything stays separated).