Question 1001239
First do the calculation inside the parenthesis:
log_4(256)= 4 Now calculate log base 2 of 4:
log_2(4)= 2 This is your answer.
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NOTE: the hand-held calculators I know only calculate natural logarithms (ln) and log base 10 (log). 
To calculate a log with a different base you have to use the formula:
{{{log_b(x)= log_d(x)/log_d(b)}}}.
Let's do one of yours, the one inside parenthesis:
{{{log_4(256)= ln(256)/ln(4)= 5.545/1.386 = 4}}} I used 3 decimals to get a more accurate answer.
Now follow this example and do log_2(4). Your result should be 2.
Once you get the hang of it it's really very easy.
J