LU Decomposition

You're given a matrix $A$ . Find $a$ and $b$ such that matrices $L$ and $U$ form the $LU$-decomposition of the matrix $A$. $$A={\begin{pmatrix} 20 & 15 & 0 \\ 16 & 68 & 56 \\ 8 & 13 & 27 \\ \end{pmatrix}}, L={\begin{pmatrix} 5 & 0 & 0 \\ 4 & a & 0 \\ 2 & 1 & 5 \\ \end{pmatrix}}, U={\begin{pmatrix} 4 & 3 & 0 \\ 0 & b & 7 \\ 0 & 0 & 4 \\ \end{pmatrix}}$$

Write down $a$ and $b$ accurate to $1$ decimal place and separated by space. For example

1.1 2.2