Volume =$l \times b \times h$ = $6 \times 5 \times 2$ = 60 $c{m^3}$

Now volume is reduced by 19%.

Therefore, new volume = $\displaystyle\frac{{(100 - 19)}}{{100}} \times 60 = 48.6$

Now, thickness remains same and let length and breadth be reduced to x%

so, new volume: $\left( {\displaystyle\frac{x}{{100}} \times 6} \right)\left( {\displaystyle\frac{x}{{100}} \times 5} \right)2 = 48.6$

Solving we get x =90

thus length and width is reduced by 10%

New width = 5-(10% of 5)=4.5