Answer:
 
  
The p value can be founded with this formula:
 
  
Since the p value is higher than the significance level provided of 0.05 we have enough evidence to FAIL to reject the null hypothesis and we can't conclude that the true mean for the Gibbs brand is significantly lower than the true mean for the competitor 
Step-by-step explanation:
Information given
 represent the mean for Gibbs products
 represent the mean for Gibbs products
 represent the mean for the competitor
 represent the mean for the competitor
 represent the population standard deviation for Gibbs
 represent the population standard deviation for Gibbs
 represent the sample standard deviation for the competitor
 represent the sample standard deviation for the competitor
 sample size for the group Gibbs
 sample size for the group Gibbs
 sample size for the group competitor
 sample size for the group competitor
 Significance level provided
 Significance level provided
z would represent the statistic 
Hypothesis to verify
We want to check if babies using the Gibbs brand gained less weight, the system of hypothesis would be:  
Null hypothesis: 
  
Alternative hypothesis: 
  
The statistic would be given by:
 (1)
 (1)  
Replacing the info given we got:
 
  
The p value can be founded with this formula:
 
  
Since the p value is higher than the significance level provided of 0.05 we have enough evidence to FAIL to reject the null hypothesis and we can't conclude that the true mean for the Gibbs brand is significantly lower than the true mean for the competitor