We want all x's on one side, all the terms in t on the other.
Divide both sides by `(x + 3)` and multiply both sides by `dt`:
Next, divide both sides by t.
Integrate both sides.
Important: dx and dt must be on top of the fraction (i.e. in the numerator).
Take "e to power of both sides":
(We let `e^C=K`, constant)
So `x = Kt - 3`.
We let `K = 7`, for illustration):
Typical solution graph `x=7t-3`.
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