exam Maths Puzzle Numerical Ability

please help me solve this equation:
one pump can fill a tank with oil in 4 hours. a second pump can fill the same tank in 3 hours. if borh pumps are used at the same time, how long will they take to fill the tank.

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The table shows the average fuel consumption (in gallons) of a passenger car between 1970 and 1996.
Please ingnore the stars...i was trying to make a table! haha!
_______________ An investment of $5000 is made at an annual simple interest rate of 5.3%. How much additional money must be invested at an annual simple interest rate of 8.5% so that the total interest earned is 6.5% of the total investment?