Classify the following as linear,quadratic,and cubic polynomials:
$(i)$ $1+x$
$(ii)$ $3t$
$(iii)$ $r^{2}$
$(iv)$ $7x^{3}$

(N/A) $(i)$ $1+x$
Since the degree of $1+x$ is $1$,it is a linear polynomial.
$(ii)$ $3t$
Since the degree of $3t$ is $1$,it is a linear polynomial.
$(iii)$ $r^{2}$
Since the degree of $r^{2}$ is $2$,it is a quadratic polynomial.
$(iv)$ $7x^{3}$
Since the degree of $7x^{3}$ is $3$,it is a cubic polynomial.