Evaluate 5+5/6-8-13+10.

How to find f'(0) ?
${\displaystyle f\left(x\right)=\frac{x^2+3}{2x-1}}$

Simplifying compound fraction: ${\displaystyle \frac{3}{\frac{\sqrt{5}}{5}}}$
I'm trying to simplify the following: ${\displaystyle \frac{3}{\frac{\sqrt{5}}{5}}}$
I know it is a very simple question but I am stuck. I followed through some instructions on Wolfram which suggests that I multiply the numerator by the reciprocal of the denominator.
The problem is I interpreted that as:
${\displaystyle \frac{3}{\frac{\sqrt{5}}{5}}\times \frac{5}{\sqrt{5}},}$
Which I believe is:
${\displaystyle \frac{15}{\frac{5}{5}}=\frac{15}{1}.}$
What am I doing wrong?

A restaurant uses ${\displaystyle 2\frac{3}{4}}$ pounds of flour to make a batch of dinner rolls. About how many pounds of flour are needed if 3 batches of dinner rolls are to be made?

Perform the addition or subtraction and simplify.
${\displaystyle \frac{1}{x}+\frac{1}{x^2}+\frac{1}{x^3}}$

Explain the difference in the process to clear fractions between the two equations.
${\displaystyle \frac{x}{3}+\frac{1}{2}=1\text{and}\frac{3}{x}+\frac{1}{2}=1}$

Compute 11/4*6+14/10+10.

Simplify ${\displaystyle \frac{4}{10}}$ if it isn't in lowest terms.