After a long$$ study, tree scientists conclude that a eucalyptus tree will grow at the rate of

$0\mathrm{.}6$ plus $6$ divided by left parenthesis t plus $1$ right parenthesis cubed$0\mathrm{.}6+6/($t$+1)3$

feet per$$ year, where t is the time$($in years$).$

$($a$)$ Find the number of feet that the tree will grow in the second year.

$($b$)$ Find the number of feet the tree will grow in the third year.