We can use the law of sines, which relates the angles and sides of a triangle.
The formula is:
\(\frac{sinA}{a}= \frac{sinB}{b}= \frac{sinC}{c}\),
where A, B, and C are angles and a, b, c are side lengths.
Let's find the missing angle. The interior angles of a triangle add up to 180 degrees, so the missing angle is 180-70-40 = 70 degrees.
Let's make a proportion and use the two 70 degrees angles and their opposite lengths. Since both sides have the same numerator of 70 degrees, we can equate the denominators together.
\(\frac{sin70}{x+25}= \frac{sin70}{6x} \\ \\
x + 25 = 6x \\
25 = 5x \\
x = 5\)
