Question 1151194
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The solution by tutor @MathLover1 is perfectly good... but it involves calculations much more complicated than necessary.  The solution can be achieved much more easily using a basic fact about similar figures.<br>
All squares are similar.  The ratio of the side lengths of the two squares is 36:42 = 6:7.<br>
In any similar figures, the ratio of area measurements is the square of the ratio of the linear measurements.  So the ratio of the areas of these two squares is 6^2:7^2 = 36:49; or, expressed as a common fraction, 36/49.<br>