book Maths Puzzle Numerical Ability

I need help solving x4 -5x2 - 36=0 I am not sure what to do with x4

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book Other Question

-4x_is 1 _ is blank there were 429 people nat a play. admission was $1 for adults and $.75 for children. the receits were $372.50. How many adults and how many children attended the play?