Analysis: this question involves a ternary linear equation;

a+B+20 = 68；

b+ C+37 = 68；

a+C+35 = 68；

Get the answer:

A = 30

b = 18；

C= 13 .

Solution idea

The basic idea of solving ternary linear equations is still elimination method, and its basic methods include substitution elimination method and addition and subtraction elimination method.

Steps:

(1) Eliminate an unknown by substitution or addition and subtraction, and get a set of binary linear equations;

(2) Solving the binary linear equations to obtain two unknown values;

(3) Substitute the values of these two unknowns into the equation with three unknowns in the original equation, find the value of the third unknown, and write the values of these three unknowns together with braces to get the solution of the ternary linear equations.