Since we know that the two triangles are similar that means we can find the ratio. The larger triangle is two times larger, we can find that out using 7/3.5 = 2. That means x + 4 = 2y and 3y = 2x. We can solve for y using substitution. We can double the first equation. 2x + 8 = 4y. We know that 2x = 3y so we can plug that in. 3y + 8 = 4y. Solving for y, gets us y = 8. Now we can plug that into any of the prior equations. I'll use 3y = 2x. 3(8) = 2x. 24 = 2x. Divide both sides by 2. x = 12.
