It says

Suppose P(X=a)=p and P(X=b)=1-p

So clearly (X-b)/(a-b) is a Bernoulli Random variable. Find Var(X).

The solution says:

p(1-p)=Var((X-b)/(a-b))1/(a-b)^2Var(X-b)=1/(a-b)^2*Var(X)=

So

Var(X)=(a-b)^2*p(1-p)

What I don't understand is how they did the part where I have underlined the equal sign (i.e. how to get out the 1/(a-b)^2 from that). Thanks.