d= dimes
n = nickels
d =n+7
n*.05+.1*d = 1.90
substitute d = n+7
.05n +.1 (n+7) = 1.9
distribute
.05n +.1n +.7 = 1.90
combine like terms
.15n +.7 = 1.9
subtract .7 from each side
.15n = 1.2
divide by .15
n=8
d=n+7
d=15
you have 8 nickels and 15 dimes
It would be .345% because to change it to a percent all you have to do is move the decimal point two places to the right.
Y2-y1/x2-x1 is the formula so lets say -4=x1 0=y1 and 2=x2 0=y2. 0-0/2-(-4) = 0/6
B : 30
95+55 = 150
180-150 = 30
