Fractions And Decimanls help me for solve math question i dont know what i do here +,-,multiply or divide?

Q. There are 42 pupils in a class . 3by4 of the boys and 2by3 of the girls travel travel to school by bus . The total number of boys and girls who travel to school by bus is 30 .





(a) how many boys are there in the class ?


(b) How many girls travel to school by bus ?

Fractions And Decimanls help me for solve math question i dont know what i do here +,-,multiply or divide?
let boys be b


let girls be g





3/4 b +2/3g =30


9/12 b + 8/12g = 30


1/4 b + 1/3 g = 12


3/12 b + 4/12 g = 12





9/12 b - 3/12 b= 6/12 b


8/12g -4/12g=4/12g


30-12=18


6/12b + 4/12g = 18





2*(6/12b + 4/12g = 18)


= b + 8/12g = 36





2*(3/12 b + 4/12 g = 12)


= 6/12 b + 8/12g = 24





(b + 8/12g) - (6/12 b + 8/12g) = 36-24


= 6/12 b = 12





b=12*2


=24 answer(a)








3/4 b =18


30-18=12 answer(b)
Reply:no of boys in the class =24


no of girls who travel by bus=12