Which rule is linear decay and also has initial value (150)?

Correct answer: \(y=150-12x\)

A linear rule has the form \(y=a+bx\), where the initial value is \(a\), found by putting \(x=0\). In \(y=150-12x\), the initial value is 150 and the coefficient of \(x\) is \(-12\), so the value decreases linearly. \(y=12-150x\) also represents decay, but its initial value is 12. Exam tip: put \(x=0\) to check the initial value, and look for a negative slope to identify decay.