Thought $-$ Objective $3-$ Comprehensive comparison of all vehicles Review your answers to the Thought Problems in this section. $($a$)$ What is the impact of increasing the before$-$tax rate of return $($R$)$ for one savings vehicle but not for another when comparing any two savings vehicles? For example, when comparing the savings account with the deductible pension, what is the impact of increasing R for the savings account if R for the deductible pension remains constant? What general rule does this suggest? $($b$)$ What is the impact of increasing the tax rate $($t$0)$ when ranking all savings vehicles? $($c$)$ What is the impact of decreasing the tax rate $($t$0)$ when ranking all savings vehicles?