Question 71362
m = the number of 15-ton silos
n = the number of 20-ton silos
{{{m + n = 30}}}
{{{15m + 20n = 510}}}
multiply the 1st by 15
{{{15m + 15n = 450}}}
subtract from the 2nd
{{{5n = 60}}}
{{{n = 12}}}
{{{m = 18}}}
check answer
{{{15m + 20n = 510}}}
{{{15*18 + 20*12 = 510}}}
{{{270 + 240 = 510}}}
{{{510 = 510}}}
OK