Answer:
Dear mcdeagon,
Answer to your query is provided below:
Magnitude of -2a-3b = -18i-6j
Explanation:
When a = 3i+9j and b = 4i-6j
Magnitude of -2a-3b will be calculated by putting value of a and b
So, -2a-3b = -2(3i+9j)-3(4i-6j)
= -6i-18j-12i+12j = -18i-6j