Evaluate the expression when =a7 and =c−4 .−a2c

It seems like there might be a mistake in your question as it's not clear. However, if you're asking to evaluate the expression -a^2c when a=7 and c=-4, here are the steps:

1. Substitute the values of 'a' and 'c' into the expression. So, -a^2c becomes -(7^2*-4).
2. Calculate the square of 7 which is 49. So, the expression now becomes -(-4*49).
3. Multiply -4 and 49 to get -196. So, the expression now becomes -(-196).
4. The negative of -196 is 196.

So, the value of the expression -a^2c when a=7 and c=-4 is 196.