To value a high growth stock, widely used is the PEG ratio indicator, which is, namely, the ratio of PE/Growth-rate. As a rule of thumb, if PEG>1, it's over valued; if PEG<1, it's under valued; and if PEG=1 it's just right.
(See for example -
https://en.wikipedia.org/wiki/PEG_ratio)
Now ALU's PE=70+x,
(1) if its earnings Growth rate = 50%, then PEG=70+/50 = 1.4x, 40% over valued;
(2) if its earnings Growth rate = 25%, then PEG=70+/25 = 2.8x, 180% over valued;
(3) If as said in the above post,
"... (prior to the result) the 2018 forward PE was 39.2x ... the 2020 forward PE was 22.6x"
then the Growth rate in the 2 years between 2018-2020 will be
(39.2/22.6)^^0.5 -1 = 31.7% p.a.
so PEG = 70/31.7 = 221%, 121% over valued.
