Help! Continuious random variable problem

Note that if we draw a vertical line at x = 3.....we have a triangle on the right with a base of 1 and a height of .25

So....the area of this triangle  =  (1/2) (base) (height)  = (1/2) (1) (.25)  = .125

So....P ( X < 3)  =   Total area -  area of the triangle on the right  =  1 - .125  = .875