I need help to work out how to solve this puzzle. The puzzle is very self-explanatory...
This is a system of 4 equations with 4 variables:
From 2nd and 4th equation:
For easier writing let's put $1/c=x$ and insert $a$ and $d$ into 1st and 3rd equation:
so $30x = 3$ or $x=1/10$
From here it is easy:
$c=10$, $a=21/10$, $d=9/10$ and $b=59/10$