Answer: 155 = 128+27
128 = 2^7 is a power of 2
27 = 3^3 is a perfect cube
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Step-by-step explanation:
This is something you'd find through trial and error.
The powers of 2 are
2, 4, 8, 16, 32, 64, 128, 256, ...
We double each value to get the next one.
The largest power of 2 that is smaller than 155 is 128
155-128 = 27 which is a cube number since x^3 = 3^3 = 27 as you've shown in the screenshot.
If the result of 155-128 wasn't a perfect cube number, then you'd have to try the next largest power of 2 (which is 64) and work your way down the list.
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Or you could work with the list of perfect cubes
1, 8, 27, 64, 125, 216, ...
Each value is of the form x^3 where x is a whole number.
Let's pick the largest perfect cube that is under 155, and subtract it
155-125 = 30 which isn't a power of 2 (refer to the list above)
Then try 155-64 = 91 which isn't a power of 2 either
Keep moving down the list until reaching 155-27 = 128 which is a power of 2 since 2^7 = 128