This is the concept of algebra, we are required to write the function representing the expression given. After the the numbers were substituted we got: 1. f(32)=120+5(32-30) given that 120, 5 and 30 are not changing in all the consecutive substitutions, it implies that they are constant. Therefore the rest are variable, hence our expression can be written as: f(x)=120+5(x-30) The above expression is a straight line equation, representing a linear expression between variables.
