A good train took 7 hours to complete its journey. For the first 3 hours, it travelled an average speed of 186km/h. What was the total distance of the journey? km

Given the position vector of the particle r(t)=(t+1)i+(t^2−1)j+2t k, find the particle's velocity and acceleration vectors at t=1

In a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina. what should be the radius of curvature of the cornea such that the image of an object 40.0 cm from the cornea’s vertex is focused on the retina?

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.