How many miles is it to the sun from earth?

Hint: In 1672, Cassini made the first rigorous and accurate scientific measurement of the Earth-Sun distance using parallax measurements of Mars. From two places simultaneously, he and another astronomer observed Mars. The distance between Earth and the Sun can be calculated once this Earth-Venus distance is known.

Complete answer:
The Astronomical Unit (symbolized as au or AU) is a length measure which as the name suggests, is usually used in astronomy. It is the mean of the distance between the Earth and the Sun.
Since the Earth moves around the Sun in an elliptical orbit with the sun at one of its focal points, the absolute distance between the Earth and the Sun continues to change continuously.
The mean distance is determined by the average distance between the aphelion (the position where the Earth is closest to the Sun) and the perihelion (position where the Earth is nearest to the Sun). Approximately 150 million kilometres is the value of 1 Astronomical Unit.
$1 a u=1.5 \times 10^{11} m$
One light year is the distance travelled by light in a span of 1 earth year. It is equal to $9.46 \times 10^{15} \mathrm{~m}$.
One angstrom is equal to $10^{-10} \mathrm{~m}$.
One Fermi is equal to $10^{-15} \mathrm{~m}$.

Note:
Since they form the basics of the topic, students must have a strong hold on the units and dimensions of different physical quantities. Such knowledge-based questions can easily lead the student not to be able to attempt a quick and easy scoring question if not properly known, or even worse to make a stupid mistake in it and lose marks. In competitive exams, these types of questions give easy marks in less time and a student who can answer such questions will definitely have an edge over others.