Math

A+B=17   (1)

B+C=16   (2)

(1)-(2)

A+B-B-C = 17-16

A - C = 1

so

A=1+C      

 

Now   

A*C = 30    so

(1+C)*C = 30

c^2+C-30=0

(C-5)(C+6)=0

C = 5 or -6

but C is positive so  C=5

so

A=1+C = 6

 

Find  B and D