Hello from MrBillDoesMath!
Answer:
x = 15
Discussion:
The triangle is an isosceles triangle so the base angles are equal. That is,
3x = 5x - 30 =>
3x - 3x = 5x - 3x - 30 => (subtract 3x from both sides)
0 = 2x - 30 => (add 30 to both sides)
30 = 2x =>
x = 30/2 = 15 (divide both sides by 2)
Regards,
MrB
P.S. I'll be on vacation from Friday, Dec 22 to Jan 2, 2019. Have a Great New Year!