What would the unit be if you calculate the rate when A= 0.30 M and b= 0.30 M. I have the calculation done right and its 1.57 x 10 to the -3 but I don't know the unit

I think that you need more information then what you are providing for someone to be of any help.

Devron is right. You need to know the order of the reaction. I copied the following from Wikipedia.

For order zero, the rate coefficient has units of mol·L−1·s−1 (or M·s−1)
For order one, the rate coefficient has units of s−1
For order two, the rate coefficient has units of L·mol−1·s−1 (or M−1·s−1)
And for order three, the rate coefficient has units of L2·mol−2·s−1 (or M−2·s−1)

To determine the unit of the rate when A = 0.30 M and B = 0.30 M, you need to consider the definition and equation that you used to calculate the rate.

In general, the rate of a reaction is expressed as the change in concentration of a reactant or product per unit time. The units for rate can vary depending on the specific reaction and the order of the reaction.

However, since you have provided the concentrations of A and B, it indicates that you are likely calculating the rate of a chemical reaction with respect to time t. In this case, the unit of the rate will be M/s (molar per second).

Therefore, the correct unit for the rate you have calculated (1.57 x 10^-3) is M/s, which indicates that the concentration is changing by 1.57 x 10^-3 M per second.