Question 1123991
System of Equations:

Let the number of pics James has = J
Let the number of pics Kelvin has = K

{{{J+K=2100}}}
{{{K+300=J}}}

Plug in:

{{{J=300+K}}}
{{{(300+K)+K=2100}}}
{{{300+2K=2100}}}
{{{2K=1800}}}
{{{K=900}}}

Kelvin has 900 Pics

If you need to know how many James has, you can plug Kelin's number back in:
{{{J=300+K}}}
{{{J=300+900}}}
{{{J=1200}}}

James has 1200 Pics