Answer:
Number of boys in the park is 36
Explanation:
Number of boys playing = x
Number of girls playing in park =

Total children playing in the park = 42
Now, accoding to the question,
Number of Boys + Number of girls = Total children in park

or,

Squaring both sides we get

or,

or,
⇒(x-49)(x-36) = 0
⇒ either x = 49, or x = 36
if number of boys playing in the park is 49,
then number of girls = 42 -49 NOT POSSIBLE
⇒ x ≠ 49
Hence, x = 36 = Number of boys
And, Number of girls = 42 - 36 = 6