Edexel Physics AS level Unit 1

A man is walking at a constant horizontal velocity of 1.2 m/s in the rain. To the man, the rain appears to be falling at a velocity of 1.8 m/s

Draw a labeled vector diagram to scale and use it to determine the actual velocity of the rain

Using the notation (eqn 4.33) given in the following webpage for the relative velocity, we are doing a vector addition to find the actual velocity of the rain.
velocity of the rain relative to ground = velocity of the rain relative to man + velocity of the man relative to ground

In maths notation,

$\vec{v}_{\text{rg}} =\vec{v}_{\text{rm}} + \vec{v}_{\text{mg}}$

https://openstax.org/books/university-physics-volume-1/pages/4-5-relative-motion-in-one-and-two-dimensions