The sum of the angles in a triangle is 180 degrees
Angle D = (4x + 1)
Angle F = (5x - 4)
Angle E = ?
Let angle E be x
The base of the of the triangle does not have the same base
4x + 1 + 5x - 4 + x = 180
Open the parenthesis
4x + 1 + 5x - 4 + x = 180
Collect the like terms
4x + 5x + x = 180 + 4
10x = 184 - 1
10x = 183
Divide both sides by 10
10x/10 = 183/10
x = 18.3 degrees