This is not the answer, but I want to tell you that I can't see what the problem says. I would help you, but I can't.
So... the radiator has 15 liters of 70% antifreeze.. but needs an 80% antifreeze
well, so, you need to drain some and put some with higher percentage, seems to be, you will end up at the same 15 liters, possible the radiator's capacity, of 80% antifreeze
so, the same amount going out, of 70% is the same amount going in, of 100% antifreeze
now.. let's use the decimal format for the percents, or 70% is 70/100 or 0.7 and so on
![\bf \begin{array}{lccclll} &amount&concentration& \begin{array}{llll} concentration\\ amount \end{array}\\ &-----&-------&-------\\ \textit{70\% sol'n, out}&x&0.7&0.7x\\ \textit{100\% sol'n, in}&x&1.00&x\\ \textit{current 70\% sol'n}&15&0.7&10.5\\ -----&-----&-------&-------\\ mixture&15&0.8&12 \end{array}](https://tex.z-dn.net/?f=%5Cbf%20%5Cbegin%7Barray%7D%7Blccclll%7D%0A%26amount%26concentration%26%0A%5Cbegin%7Barray%7D%7Bllll%7D%0Aconcentration%5C%5C%0Aamount%0A%5Cend%7Barray%7D%5C%5C%0A%26-----%26-------%26-------%5C%5C%0A%5Ctextit%7B70%5C%25%20sol%27n%2C%20out%7D%26x%260.7%260.7x%5C%5C%0A%5Ctextit%7B100%5C%25%20sol%27n%2C%20in%7D%26x%261.00%26x%5C%5C%0A%5Ctextit%7Bcurrent%2070%5C%25%20sol%27n%7D%2615%260.7%2610.5%5C%5C%0A-----%26-----%26-------%26-------%5C%5C%0Amixture%2615%260.8%2612%0A%5Cend%7Barray%7D)
so.. let's subtract, from the current solution, 0.7x and add 1x or x, our antifreeze concentration amount, should be 12 though
10.5 - 0.7x + x = 12
solve for "x"
RS=70. It helps if you draw a picture of a line and plot the data but you just have to add them in this case:17+52=70. Hope this helped!
The answer is the last one 8
- 4 + -2 + -6 = -12.
If his total score was -10, then his final score would be 2, assuming that "combined total score" means the sum of all the scores rather than the average of the scores.