Question

I’m not sure how to set up this algebra equation (#6) thanks :)

Answer 1

to get the average of any data set, we simply divide the SUM of the data by the AMOUNT of values, so in this case we have 6 exams, therefore

$\bf \cfrac{66+72+80+45+59+x}{6}\ge 65\implies 322+x\ge 390\implies x\ge 68$