Mr. Deane will spend $1.4/liter x 10 liters = $<<1.4*10=14>>14 for the 10 liters of gas today.
The price of the gas per liter on Friday will be $1.4/liter - $0.4/liter = $<<1.4-0.4=1>>1/liter.
So, he will spend $1/liter x 25 liters = $<<1*25=25>>25 for the 25 liters of gas on Friday.
Thus, Mr. Deane will spend a total of $14 + $25 = $<<14+25=39>>39 for the 35 liters of gas.
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