book Maths Puzzle Numerical Ability

i know this forum is for albebra but i was hoping someone could possibly help me with a statistics problem.

in hypothesis testing when you have n>30 ex: n=36>30, how do you get

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book Other Question

how do you solve 2 with 3 exponent.5 with 2 exponent okay i dont know how to do the whole typy in htingy but it says
"the square root of x+2 = the square root of 3x-6 so is it 4?