Standing waves in a spring [closed]

So the question goes like this

A string 1 m long is fixed at one end. The other end is moved up and down with frequency 15Hz. Due to this , a stationary wave with four complete loops , gets produced on the string. Find the speed of the progressive wave which produces the stationary wave [ Hint: Remember that the moving end is an antinode.]

basically any other text book homework question but litrary every answer i can find on internet is using the relation $$\lambda = \frac{L}{2}$$ ($$\lambda$$ is wavelength of standing wave formed)

but it seems wrong as the question clearly states one of the ends is an antinode which means $$\lambda$$ should be $$\frac{4}{7}$$ times the length of the spring, Am i missing something here or is litrary every website copying other answers without verifying them.

The wavelength is not related by either of those two. It's $$\lambda = \frac{2*L}{n}$$ where $$n$$ is the number of loops. Since it's 4 loops PLUS the half loop required to generate the string with an antinode, $$\frac{2*1}{4.5} = .\overline{4}\text{meters}$$
The speed of this wave is then $$v = \lambda f = .\overline{4}\text{m}*15\text{Hz} = 6.\overline{6}\frac{m}{s}$$ I'm not sure where you got $$4/7$$ from