book Maths Puzzle Numerical Ability

I dont quite understand ow to solve this problem.

Solve for a H=18t+1/2at(this last t is supposed to be squared)

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x squared +x -12 multiply by x squared +5x +6 divided by x +3
x squared +x -30 x squared -2x -3 x squared +7x +6 Question: the sum of four numbers is 22. the first number is twice the difference of the second and fourth numbers. the second number is 5 times the difference of the third and f