it should be

(a=3*5，a*4)，a+5。

Comma expressions pay attention to two basic knowledge:

1. Comma expressions operate from left to right.

2. The value of the comma expression takes the value of the rightmost expression in the comma.

Now look at (a = 3 * 5, a * 4), comma expression A+5,

First of all, for (a=3*5, a*4) and a+5, calculate from left to right (a=3*5, a*4).

(a=3*5，a*4)

This comma expression calculates a=3*5 from left to right. This is an assignment statement, which deals with a=3*5= 15.

Calculate a*4 again, at this time a= 15, so a*4=60, but note that this expression does not assign a value to a, but is just a multiplication operation.

According to the principle that the value of comma expression takes the value of the rightmost expression in comma, the value of (a=3*5, a*4) is 60.

Look at a+5,

In the previous operation (a=3*5, a*4), a has been assigned to 15, so here a+5= 15+5=20.

So the value of expression a+5 is 20.

According to the principle that the value of comma expression takes the value of rightmost expression in comma,

Expression (a = 3 * 5, a * 4), the value of a+5 is the value of a+5, which is equal to 20.