Study some exceptions for adjectives.
Запомните прилагательные, степени сравнения которых образуются не по правилу.

• Good – better – the best

• Bad – worse – the worst

• Little – less – the least

• Many/much – more – the most

• Old – elder – the eldest (когда говорим о членах семьи)

• Far – farther – the farthest

The train ticket is the least expensive.

Travelling by plane is the best variant.
Рис. \(1\). Travelling by plane
Who is the eldest in your family?
Рис. 1. Travelling by plane, 2019, https://pixabay.com/images/id-4516478/ Pixabay License CC0 Free for commercial use No attribution required