Help

[lime crag]

I need it to help me with my quiz tomorrow, any help will be appreciated. I am in 9th grade if that makes it simpler

[limpid onyx]

Sides of an equaliterial triangle are equal
7x - 15 = 3x + 5 = 4x

[lime crag]

so all I need is to solve for x right?

then I will get my answer?

[limpid onyx]

Yea