Simplify the following expressions and comment on the nature (rational or irrational) of each final result. Show each step of your working.
a. (i) (35−20)+(45−25)
b. (ii) 3−51
c. (iii) Construct an expression that uses the number 5 exactly once together with any two rational numbers so that the overall value of the expression is a rational number. Justify your answer by computation.