The formula for area of a triangle is: 1/2 x base x height.
You are given the height of 4 and the area of 4.
Replace those in the formula and solve for x ( base)
4 = 1/2 x base x 4
Divide both sides by 4:
1 = 1/2 x base
Multiply both sides by 2:
2 = base
x = 2