Hello, I need help for the following problem:

You are working with the marketing team for a FMCG firm that produces shaving cream. The team believes that sales of some of the products are closely related to sales of other products. They want you to explore this in a little more depth for two products, SKU 123 and SKU 456. Unfortunately, all of the base sales data for these products has been destroyed. All that you have is the weekly summary data:

Data. SKU123. SKU456.
Mean 878. 991
SD. 116 278
Sales price 12.5. 7.75

For the expected weekly revenue, I got the correct result of 18655.25 $ by multiplying the means with the sales prices.
Now the question is to calculate the standard deviation of this weekly revenue -assuming that the correlation is 0.76.

It is not correct to just calculate the square root of 12.5^2*116^2+7.75^2*278^2
So what do I have to calculate?

Thanks in advance