The diagram below shows the positions of the earth, moon, and sun. what is the date?

a) march 21
b) june 21
c) september 23
d) december 21

Answer is: B) June 21.
This is summer solstice or midsummer.
Summer solstice occurs when a planet's geographical pole on Northern Hemisphere is most inclined toward the Sun. Earth's maximum axial tilt toward the Sun is 23.44° and the Sun reaches its highest altitude of the year on the summer solstice.

Yes you are correct use the scientific method