He didn’t follow PEMDAS which is the an acronym for the order of operations. according to pemdas the first step is parenthesis (which is the p in pemdas) there fore the first step is to add the 1 and the 2
then since there are no exponents you multiply so you multiple 5(3) which is 15
then you can add all the number left to right
so 15+2+3= 20
so the answer is 20
hope this helped
let me know if you have any questions
X^2+8x+19+39/(x-2)
I cant show how to use synthetic unless I attach a file
2 gallons 25% of 4 is 1 so there is about 1 gallon of pure in there no so adding two will make 3 gallons of antifreeze bringing total to 6 gallons 3/6 = .5 boom bam 50%
Do both as equation it will make it easier for her