Which interaction involves only one of Earth's spheres?

The focal length of a relaxed human eye is approximately 1.7 cm. when we focus our eyes on a close up object, we can change the refractive power of the eye by about 16 diopters. (a) does the refractive power of our eyes increase or decrease by 16 diopters when we focus closely? explain. (b) calculate the focal length of the eye when we focus closely.

What is the average speed of a car that travels 40mph for 1 hour and 60 mph in another hour will mark brainliest

It is really hard for me right know