A scientist mixes water (containing no salt) with a solution that contains 35% salt. She wants to obtain 105 ounces of a mixture that is 15% salt. How many ounces of water and how many ounces of the 35% salt solution should she use?

90

Step-by-step explanation:

Start with changing 35% and 30% to a decimal.

35% = .35%

30% = .30%

Then multiply 105 by .30%. ( but don't put the percent sign in the calculator when multiplying)

105 x .30% = 31.5

Then you want to divide 31.5 by .35%

31.5 /  .35% = 90

$53.50

step-by-step explanation:

you have to subtract the amount of money chuck earned ($72.50) by the cost of the gas for the mower ($11.25) and the new string for the trimmer he bought ($7.75).

72.50-11.25=61.25

and then subtract $61.25 by the second thing he bought (the new string for the trimmer)

61.25-7.75=53.5

so in total it's $53.50 (53 dollars and 50 cents)