Mr. Mole left his burrow and started digging his way down.
A represents Mr. Mole's altitude relative to the ground (in meters) after t minutes.
A= -2.3t - 7
How fast did Mr. Mole descend?

step-by-step explanation:

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cross multiplying, we get :

⇒ (3) × (5) = (9) × (x)

⇒ 15 = 9x

multiplication is multiplication.   it might feel harder depending on what level of math you are in, but generally it will be the same old stuff, while implementing some new concepts and methods of solving work.