Answer:
(49 - 29) + 1 =(50 - 29)
Step-by-step explanation:
The 20 comes from the subtraction of 29 in both sides of the previous step equality. In the following, I transcript the complete procedure and I add the step that you need to understand why 20 appears (in bold numbers):
29+20=49
49+1=50
(49 - 29) + 1 =(50 - 29)
20+1=21
50-29=21
hence, it was only nesseraty to subtract 29
