微積分應用問題

Two cars start moving from the same point. One travels south at 60 km/hr and the other travels west at 25 km/hr. At what rate is the distance between the cars increasing three hours later?A rectangle has its base on the x-axis and its upper two vertices on the curve of . Find the largest area of the rectangle(這題我算都是16). 不知道哪裡算錯麻煩幫我解答..
1.y=[(25T)^2 (60t)^2]^1/2=[(4225)^0.5]*tdy/dt=(4225)^(1/2)=65
奇怪為啥補充都會不見第2題有點怪一矩形底邊在x軸上上方2頂點在曲線上(啥曲線沒方程式阿)求最大面積
第一題 2者距離是直角三角形ㄉ關西所以距離與時間ㄉ函數y=[(60t)^2 (25t)^2]^0.5
y=12-x^2 x= /-(12-y)^0.5面積 f(y)=2[(12-y)^0.5]*yf