The problem is about functions, specifically, replacing a given value.
The expression f(3a - 4) indicates that x = 3a - 4, so we need to replace the variable with this expression.
[tex]f(x)=5x+1\rightarrow5(3a-4)+1[/tex]As you can see, we changed the variable for the given expression. Now, we use the distributive property
[tex]f(3a-4)=15a-20+1[/tex]At last, we reduce like terms
[tex]f(3a-4)=15a-19[/tex]
