What do you mean about his
Pemdas
Parentheses exponents multiplication divide add subtract (7+5)=12
12+4•13-2 4•13= 52
12+52-2
64-2
The answer is 62
Fractions need common denominator to add or subtract them because without denominators a fraction is not a fraction, it is a whole number
Example - 2/8 is a fraction
but 2 is not a fraction
90/3 parts of silver = 30 times multiplied by
tin = 12 × 30 = 360g
lead = 8 × 30 = 240g
12.5 / 23 = 0.5434 parts per metal
tin = 12 × 0.5434 = 6.5kg
lead = 8 × 0.5434 = 4.5kg
silver = 3 × 0.5434 = 1.5kg