exam Maths Puzzle Numerical Ability

i do not understand this show me please?
(2r-3s)(4r^2+6rs+9s^2)

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exam Other Question

three times the largest of three consecutive odd integers is three less than twice the sum of the other two integers. find the integers. Solve the system by addition.
4x - 9y = -14
x + 2y = 5