Question 1050457
1.{{{15B+10C+5L=1200}}}
2.{{{15B+20C+5L=1800}}}
3.{{{5B+30C+5L=2150}}}
Subtract eq. 3 from eq. 1 and eq. 2,
{{{15B+10C+5L-5B-30C-5L=1200-2150}}}
{{{10B-20C=-950}}}
4.{{{B-2C=-95}}}
and
{{{15B+20C+5L-5B-30C-5L=1800-2150}}}
{{{10B-10C=-350}}}
5.{{{B-C=-35}}}
Now subtract eq. 5 from eq. 4,
{{{B-2C-B+C=-95-(-35)}}}
{{{-C=-60}}}
{{{C=60}}}
So then working backwards,
{{{B-60=-35}}}
{{{B=25}}} 
and finally,
{{{5(25)+30(60)+5L=2150}}}
{{{125+1800+5L=2150}}}
{{{5L=225}}}
{{{L=45}}}