book Maths Puzzle Numerical Ability

Is this corect:if rank of matrix A is <= n-2 than rank of adj(A)=0

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1. -13 - 20 = 3x + 15 - 2x
2. y/-2 = -8 + 3squared
3. -15/3 = -2(5x) - 6x
4. -x = 42

I am so confused, Please HELP ME. please help me solve these following questions:
simplify the following radicals. :
squar foot of 50=?
squar foot of 325=?
squar foot of 96=?
squar foot of 256=?