I'm looking for a test and need some help ..

Variable 1: value (continuous)

Variable 2: expectation (continuous)

Dependent variable: performance

My hypothesis: high value and low expectation lead to lower performance than low value and low expectation.

How do I test this? I thought to use a t-Test, but I have no clue how to split my variable into high and low? My next thought was to use simple slope, but there are no statistical prove (only graphically).

Is there any solution?

Thank you all