Calculating starting mass for combining 2 different concentrations with a fixed final weight

We would like to know what weights of each input product is required in order to achieve a certain % at a fixed final weight.

For example:
We have an order to produce a product at 75% concentration with a fixed total output. To create this concentration, we use a combination or 2 different percentage products. What weight of each product would be required to achieve the total weight at the correct %?
Variables we would have are as follows:
Final Total Weight
Final required %
Input 1 %
Input 2 %
Data results from the calculator would be Weight of Input 1 and Weight of Input 2

Current example I have is that we need to achieve a total weight of 5000kg with 75% concentration. We will use either 50% and 85% or 65% and 85% to create the final concentration.