You add the two numbers and divide them by two
<span>Equation:
silver + silver = silver
0.45x + 0.60(40-x) = 0.48*40
----------------
45x + 60*40 - 60x = 48*40
--------
-15x = -12*40
x = (4/5)40
x = 32 lbs (amt of 45% slloy needed)
40-x = 8 lbs (amt of 60% alloy needed)</span>
The gradient formula is (y2-y1)/(x2-x1) aka rise/run, where by (x1,y1) and (x2,y2) are two points on the line.
In this case, the gradient
= -5-(-2))/(2-(-2))
= -3/4
