Your answer is :
P = K * x where P is partial pressure K is Henry's constant and x is solubility
775 torr = K L·torr/mol * 0.0.0347 mole / liter
K = 775 / 0.0347 = 22334 L·torr/mol
in the second solution we have
1670 = 22334 * x
x = 1670 / 22334
= 0.075 moles CO2 per liter of water.
Hope this helps :)
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