exam Maths Puzzle Numerical Ability

hi....
can you please help me with this?
what is log (1/4) to the base 2?

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exam Other Question

</a> Please help us solve this equation:

4. One more than the difference between 18 and 7 times a number is -9

This is what we have tried:

7n + 18 +1 = -9
7n + 19 = -9
7n = -28
n= -4

Is this correct?