In which step did Helena make an error

What is sin 7x/4 ? i need on this urgent trig

Omar is going on a road trip! the car rental company offers him two types of cars. each car has a fixed price, but he also needs to consider the cost of fuel. the first car costs $90 to rent, and because of its fuel consumption rate, there's an additional cost of s0.50 per kilometer driven.

For what values of x is x2 + 2x = 24 true?