There can be boosts to the weapon power due to techs. The screen you are using doesn't show all of the boosts.
Here is a screenshot of one of my ships using the same screen you did.
It shows 6 weapons with 11 attack each, but the total is 73.8.
When I go back to the galaxy screen, select the ship and look at the information in the lower-left corner, the value is 73. That's because some locations don't have space for all the digits (NOTE: most locations will truncate the value, but some may round it up). When I put the cursor on the number for kinetics, I get more information, as shown in this screenshot.
This still doesn't show all the boosts, but it does show a summary of all the boosts. The calculation is as follows:
6 weapons at 6 base attack each = 36
techs give a total of +5 to the total attack, so new total attack is now 41
techs also give +80% to the new total attack, so total attack in now 41 + 80% = 41 + 32.8 = 73.8
To see all the boosts, put the cursor on the ship in the galaxy screen to get a tool tip about it. Then hold down the shift key and move the cursor to the kinetic attack value in that tool tip to get another tool tip with all the information about the boosts as shown in this screenshot.
This shows 5 techs that each add 1 to the total attack value and 8 techs that each add 10% to the total attack value.
If you hold down the shift key and move the cursor to any of the techs listed, you will get more information about them.
