Question

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Answer 1

Ab + c = d

In other words, you can put it like this:
1(ab) + 1c = 1d

Since our answer choices, let's try to get a by itself.

ab + c = d
Subtract both sides by c.
ab = d - c
Now, a is being multiplied by b, so we need to perform the opposite order of operations (divide).
Divide both sides by b.

You're left with:
a = (d - c)/b

Your answer is D.)

I hope this helps!