Three terms , 19-6x , 2 + 4x , 6x + 1, are in arithmetic progression .

a) calculate the value of x .

So therfor from 19-6x to 2+4x the diffence if the same as the diffence between 2+4x an d6x+1

so (2+4x)-(19-6x)=(6x+1)-(2+4x)
add like terms
2+4x-19+6x=6x+1-2-4x
10x-17=2x-1
add 17 to both sdies
10x-2x+16
subtract 2x form both sdies
8x=16
divide boht sdie syb 8
x=2

x=2
therfor the terms are
7, 10, 13

3/4 * 4 = 3 miles in 4 days. you can look at it as a decimal/money to to help 3/4 is .75 and .75+.75+.75+.75=3.00 hope it helps and explains how to get the answer.