A decimal point is a dot or period that is placed after a whole number. Every number has a decimal point. For example, 1.243 has one. Also, 5. has a decimal point. They are just sometimes invisible. When you use a decimal point, it means that the number has a part of something added to it.
Both triangles that are given (with right angles) lie in plane m, proving that AC is perpendicular to plane m. As angle acd is from a triangle that shares the common perpendicular, it too is a right angle
Matter is anything that takes up space and has mass.
23.1 can be estimated to 23 rounded to 20.
19.24 can be estimated to 19 rounded to 20.
The answer would be 42 which would be rounded to 40.