Let x = pounds of earl grey tea
Let y = pounds of orange pekoe tea.
The total pounds is 400, therefore
x + y = 400 (1)
The new blend sells for $3.50 a pound, so the revenue is
400*3.50 = $1400.00
The cost of mixing the two teas matches the revenue, therefre
4x + 2y = 1400
or
2x + y = 700 (2)
Subtract (1) from (2).
2x + y - (x + y) = 700 - 400
x = 300
y = 400 - x = 100
Answer:
300 pounds of earl grey tea and
100 pounds of orange pekoe tea.