You can't output a float rect to a steam. You can output their components individually, however e.g. top, left, width, height.
However, since the code you provided isn't working (does it fail to compile?), instead of:
if(equationsButtonText.getLocalBounds().contains(event.mouseButton.x, event.mouseButton.y))
try
if(equationsButtonText.getLocalBounds().contains(sf::Vector2f(event.mouseButton.x, event.mouseButton.y)))
It would be helpful if you provided the errors that you are getting.