Question 861722
let x be tens and y be fifties, then
x + y = 89
10x + 50y = 2850
solve first equation for x
x = 89 - y
substitute for x in second equation
10(89-y) + 50y = 2850
890-10y +50y = 2850
40y = 1960
y = 49
substitute for y in first equation
x + 49 = 89
x = 40
there are 40 tens and 49 fifties
substitute in second equation to check answer
10(40) + 50(49) = 2850
400 + 2450 = 2850
2850 = 2850
our answer checks  :-)