Final answer:
The expression 18t+9 is factorised by extracting the common factor of 9, resulting in the expression 9(2t+1).
Step-by-step explanation:
To factorise the expression 18t+9, we look for a common factor that can be taken out of both terms. Here, the number 9 can be factored out, resulting in the expression taking the form 9(2t+1). When we factor out the 9, we divide each term in the expression by 9, resulting in the first term being 2t (since 18t divided by 9 equals 2t) and the second term being 1 (since 9 divided by 9 equals 1).
The correctly factorised expression is thus 9(2t+1). It's important to remember that factorising an expression involves expressing it as the product of its factors. In this case, 9 is a common factor that simplifies the expression into a multiplication of easier terms to work with.