The expression :
[tex]\frac{1}{7}r+3(\frac{1}{7}r)[/tex]gives the number of pages Eliza read in those three days. If r=357, then we have that:
[tex]\frac{1}{7}(357)+3(\frac{1}{7}\cdot357)=51+153=204[/tex]She read 204 pages on those days. Therefore, the answer is B.