Question 985346
Let S be the number of pounds of sunflower seed. The total of the result will be {{{150+S}}}

{{{150*0.5  + S*1.4  = (150+S) * 0.8}}}
{{{75 + 1.4S = 120 + 0.8S}}}
{{{0.6S = 45}}}
{{{S = 75}}}

Add in 75 pounds of sunflower