book Maths Puzzle Numerical Ability

I am having dificulty solving logirithms once I put them in exponential form and vice versa. Here is the question I am confused on LOGx 16=4/3

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book Other Question

coin collection worth $2.90 contains nickels, dimes, and quaters. There are three times as many dimes as there are nickels, and the number of quarters is 2 more than the number of nickels 3x2 +x -2 =0

I only need to solve this using QF and don't need to find the discriminant.