The northern part of the midwest is referred to as the “rust belt” because of its cold temperatures and generous precipitation

"Rust Belt" is a term for upper Northeastern United States region and other like the Great Lakes, and the Midwest States, referring to economic 
decline, population loss, and urban decay due to the shrinking 
of its once powerful industrial sector.

Argon, carbon-14, and carbon-12

Amath expression is a collection of one or more terms, which are separated by the signs ( + , - , x , / ).example :   8+b8+b  or  a−3a−3in algebra, an equation is a mathematical statement with two expressions where, each expression is separated by an equal (=) sign. variables can be present on both the sides of the equality (=) sign and we use letters to denote such variables.example 1:   x=4+2x=4+2  , [here, we can observe that the variable is present only on one side of the equation].example 2:   2x+3=x+42x+3=x+4  , [here, we can observe that the variables are present on both side of the equation].