Consider the following financial producuts that both generate interest via simple interest rates per annum:

X: Principle $=$ $$320,$ Rate $=12\mathrm{.}4\%$

Y: Principle $=$ $$870,$ Rate $=???$

What interest rate should Y have to have an equal growth rate to that of financial product X$?$ Give answer as a decimal $($i$.$e$.12\mathrm{.}34\%$ should be given as $0\mathrm{.}1234)$