4.2x - 1.4y = 2.1 |multiply both sides by 10
42x - 14y = 21 |subtract 42x from both sides
-14y = 21 - 42x |change signs
14y = 42x - 21 |divide both sides by 14
y = 3x - 1.5
Because a rational number is basically a fraction or decimal form
Answer is you need to multiply 8 2/3 x 5 3/4 = 49 5/6
