The diagram shows that the total number of buttons with ¾ inch length is 3.
So, if she lines all the ¾ inches buttons, then the total length will be
= ¾ inches × 3
= 9/4 inches
= 2 ¼ inches
57 times 71 = 4047 Hope that helps!
If you choose to fully simplify this expression, then the answer is b^3
If you just want to convert to rational exponent form, then the square root will be replaced with an exponent of 1/2. The rule is sqrt(x) = x^(1/2)
So,
sqrt(b^6) = (b^6)^(1/2)
which can be written as

note how the exponents 6 and 1/2 multiply to 3, which is why the fully simplified version is b^3