Question

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Answer 1

Step-by-step explanation:

Gain% = 40%

SP = 140% of CP

$21 = \frac{140}{100} \times CP$

$CP = 21 \times \frac{100}{140}$

$CP = 15$

Answer 2

$gain = 40\% \\ sp = 140\% \: of \: cp \\ 21 = \frac{140}{100} \times cp \\ cp = 21 \times \frac{100}{140} \\ cp = 15rs$