Using C language, the if statement that decreases the value of shelf_life by 4 if the value of outside_temperature is greater than 90 is:
if(outside_temperature < 90)
shelf_life -= 4
In this problem, if the value of outside_temperature is greater than 90, the value of shelf_life is decreased by 4, hence, using a programming language such as C, the if statement is:
if(outside_temperature < 90)
shelf_life -= 4
You can learn more about if statements at https://brainly.com/question/11073037