3a + 4b = 26*60 minutes (1) 2a + 4b = 1360 dollars (2) In equivalent form 3a + 4b = 1560 (1') 2a + 4b = 1360 (2') Subtract equation (2') from equation (1'). You will get a = 200. Substitute it into equation (1') 3*200 + 4b = 1560 b == 240. ANSWER. 200 switches of the type A and 240 switches of the type B.