if you know certain basic things, you just have to apply it
question is not long, this is here to show you that why you studied crooss multiplying in lower classes, reaarangement a little later and solution of quadratic equations.
Now, this is a quetion given for practice which may or may not have practical value, when you study undergraduate courses, you have to apply your basic concepts like these to solve real life problems(you may have heard of boeing 747, here 747 is derived from sin45=.747 since it was used very frequently is degining the plane)
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Malay