A particle travelling along a straight line travels the first $50 \mathrm{~m}$ with a uniform velocity of $5 \mathrm{~m} \mathrm{~s}^{-1}$, travels at a uniform velocity of $8 \mathrm{~m} \mathrm{~s}^{-1}$ for the next $5 \mathrm{~s}$ and travels at a uniform velocity of $12 \mathrm{~m} \mathrm{~s}^{-1}$ for the next $10 \mathrm{~s}$.
(i) What is the average velocity of the journey?
(ii) If the last part of the journey (during last $10 \mathrm{~s}$ ), was performed at a constant acceleration of $2 \mathrm{~m} \mathrm{~s}^{-2}$ from an initial velocity of $8 \mathrm{~m} \mathrm{~s}^{-1}$, what is the average velocity of the journey?