4/5 simplified is 0.8
2/3 simplified is about 0.6666 you can round it up to 0.7
At least do number 3 so I can help with the rest. That ok with you?
No, because the hypotenuse needs to be three. It would be true if the lengths were 2, 2, 4
N=12.5(at time t=t) Here half life
No=25
K=12.05
Simple exponential equation where you need to calculate
Your answer should be 5.75225876