Answer:
(12, 9)
Step-by-step explanation:
Please enclose fractions inside parentheses in cases such as this one. You meant b = (3/4)a, not b = 3/(4a).
To solve this system, subst. (3/4)a for b in the 2nd equation, obtaining:
a + (3/4)a = 21.
Mult. all 3 terms by 4 to eliminate the fraction 3/4:
4a + 3a = 84
combining like terms: 7a = 84
Solving for a: a = 84/7 = 12.
If a = 12, b = (3/4)a = (3/4)(12) = 9
The solution is (12, 9)
