There isn't a formula, per se. You use proportions in this case, which is the process of equating two ratios. That being said, we get:

, with B being the number of burgers produced.

128.3B = 60 * 144 -------- Cross-multiplying

B, or number of burgers =  = 67.3421668  ≈  burgers



Be reminded that since time is less (60 < 128.3), then number of burgers produced will be less also: a little less than half, actually. 

As seen above it is indeed less than  of 144, or less than 72



Another method, not using PROPORTION:

If 144 burgers can be produced in 128.3 minutes, then  = 1.122369447 burgers can be produced in 1 minute

If 1.122369447 burgers can be produced in 1 minute,

then 1.122369447 * 60, or 67.3421668 (round down to 67) burgers can be produced in 60 minutes 

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