book Maths Puzzle Numerical Ability

the answer to the following should be 4/3a, however, I cannot understand how - please help! Thank you!!

1/1.5 + 1/1.5=

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book Other Question

Solve the quadratic equation by factoring and applying the property "ab=0 if and only if a=0 or b=0"

(x^2)-4x-21=0
14xsquared + 35x + 21 / 12xsquared + 30x +18

cant figure out how to do it