By adding Friday and Saturday, Alexandra bought 12+8=<<12+8=20>>20 magazines
On Sunday she buys 8*4=<<8*4=32>>32 magazines
Before her dog got to them she had 12+8+32=<<12+8+32=52>>52 magazines
After her dog chewed up some she had 52-4=<<52-4=48>>48 magazines
#### 48