I think you just have to add all of the totals up??
It takes the son one and half hours to clean the house. To find this you need the equations F+S=2 and F+1=S. (F=father and S=son) You take the F+1 and substitute it in for S in F+S to get F+(F+1)=2. Then you combined like factors, 2F+1=2, and simplify to get F=.5hr. After this you plug .5 in to F+1=S to get (.5)+1=S, meaning it takes the son 1.5 hour to clean the house.

just a plain vanilla substitution
I would go with C because if you do A then its all new students and thats one view D is the same. C seems like the best choice.
Answer:

Step-by-step explanation:
Let x be the percentage then...

Start by dividing both sides by 4:

Simplify the fraction:

Then, multiply the fraction by 50/50, so we can get a number over 100 (that number would be the percentage). Note we can only multiply it by 50/50 since it is essentially multiplying the fraction by 1.
