Say, if the specs are at 5 V and 25 °C and I have to use the part at 7.5 V and 50 °C and I have two separate curves for voltage and temperature, how can I combine them?

Say, if the specs are at 5 V and 25 °C and I have to use the part at 7.5 V and 50 °C and I have two separate curves for voltage and temperature, how can I combine them?