Do you want to display 7.5 or 7.2?.... I am assuming you had a typo an you want to display 7.5 from the 0.75V on the microcontroller
So you are going to need a ADC (analog to digial converter), normally a microcontroller has its own build in. Learn how to set it up. The PIC18F2320 has a -bit ADC. So if you use the 10-bit ADC then you know that your steps are 2^10=1024, assume voltage reference of 5V, so 5V/1024 is 4.8mV, or 0.0048V increments.
So after the conversion your 0.75V will be 156. So what you need to do is multyply this number by 48, scaled version of 4.8mV.
Then all you do is spit out the each number to the LCD and make sure you put the dot in the right place according to the scales 4.8mV version.
Ivancho