The distributive property states that when multiplying a term with a sum multiply into each term within the sum. Here you have a sum. You’ll reverse the distributive property by factoring our a term which could multiply into each. 60x and 24 both have 12 as a factor. This makes the expression 12(5x-2) = 60x-24.
If we replace every copy of x with t, then we go from this
F(x) = 3x+5
to this
F(t) = 3t + 5
All we've done really is change the letter. We still are dealing with a variable. We're told that F(t) is equal to 26, which would allow us to replace the "F(t)" with "26" in the second equation above.
So we now have the equation 26 = 3t+5 which is the same as 3t+5 = 26
