Hi can you help me to solve this problem? but without theory stochastic. I need to use transformations and probability theory. thank you

Let X1 and X2 be items of a random sample from a distribution with p.d.f. (density function) f(x)= 2x , 0<x<1 , zero elsewhere. Evaluate the conditional probability Pr(X1<X2|X1<2X2)